Combi Boiler Thermostat Wiring

Combination boilers and connecting thermostats to them, including Hive and Nest. Also covers volt free contacts and why mains voltage must not be connected to some boiler terminals.
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[@roaming12uk1]

Some people enjoy reading, playing golf or walking. Call me sad but I thoroughly enjoy watching and listening to your videos - even when I don't understand!!! This may be 5 years old but truly enjoyed it. Thank you John

[@enquire422]

If JW were too knock on my door, I'll be listening to every word he says!

[@pjennings4940]

Thanks for this. After 1.5 hours of instalation guides, this video game me what I needed to confidently install my WiFi thermostat. A1 information

[@atanasiomartinez]

Thank you so much for your brilliantly informative teaching. Your precise and detailed information have both educated and saved me more than once. Much appreciated.

[@keithblacknell957]

Just to say thanks for a well explained video. Helped me to figure out I needed to use the common in the reciever, everything now working 👍

[@lucyhunter5667]

Engaging and informative. Never skipped any of this video. You should have your own slot on TV.

[@astront917]

spot on,ive just purchased a hive single channel and wanted an explanation on the wiring,i didnt understand which connections to use, now i understand 1 and 3, thank you.

[@denisberarie1912]

Hi John, Thank you for your video. I have an old combi boiler that the thermostat was never wired properly. I bought a new wireless relay and thermostat and managed to wire the system correctly. It is now working fine. I truly appreciate your videos. I am a qualified domestic installer but don't work as an electrician at the moment. However, I do all my electrical work myself. I am nowhere as intellectual as you. I envy your knowledge. Thank you very much for your teaching.

[@Richardincancale]

Hi John, your description is spot on for older systems like mine - a Bosch combo installed over ten years ago to which I added a Nest thermostat / programmer works well. New boilers often support ‘Opentherm’ which is a way for the thermostat to control the output of the boiler to optimise the warm up and maintain it. It would be worth having a look at that as I believe it is not always as ‘open’ as promised... Keep up the great videos!

[@TheDickPuller]

Dingo Nates ‘Opentherm’ is only one of 26 digital protocols used in CH controls, the variety & functions are all different. Opentherm is a very basic one, adopted by a few boiler manufacturers trying to unify CH controls & boilers. It’s a basic protocol, with only the boiler & thermostat speaking to each other, so very limited in performance. Other systems are ‘Bus’ like systems, where the data can be read & distributed through all components. It’s like a Bus Route, the info can stop & start at anything connected to it.

[@tealgopher]

Thanks for this video. I was slightly nervous about installing a new thermostat until I came across your explanation. But the way you described it just made it click for me.

[@mikea2567]

What happens when my receiver is buzzing? This is an ESI thermostat receiver only 2 years old. Suddenly started buzzing.

[@Chufteh]

Great video JW. Clear, concise and thorough.

[@chrisccs2112]

By far the best video on boiler wiring I have seen on youtube. Thanks John!!!

[@cartersn67]

Many thanks John, this really helped me fit a wireless thermostat to a Vaillant boiler

[@808GT]

Thank you! Perfectly explained.

[@doctorelectric470]

Good video John, I've got to connect up a boiler & thermostat tomorrow, not done one for over a year so it was good to have a reminder, cheers

[@amlyad2633]

This was very helpful and it really calmed my nerves for thermostat to boiler connections. Thank you so much!

[@mikmik4205]

John you have some of the best video series to the point no crap thanks

[@ApacheSenzala]

I absolutely love this channel. You are a national treasure

[@johnmac8084]

Very clear explanation JW. I'd like to see you do a video on making terminal connections safely. As a heating engineer who does mostly service & repairs, I come across a lot of systems where people have screwed 2 or 3 flexes together and stuffed them into a terminal strip that's too small, so that only a gentle tug is needed for the wires to fall out. I also find bits of copper flex wire sprinkled over PCBs in boilers. I always tin the wires myself. If people don't have soldering skills I guess they could crimp on bootlace ferrules. Some people tell me this is too much trouble, but I find, once done, the job goes quicker and there are no dodgy connections. The other trouble with screwing wires together is, it's not easy to remove some to test or replace components. I also find people over-tighten the terminals. Of course you don't want loose connections, but I find wires that have been crushed to half their CSA. What are your thoughts on this JW? Please do a video on this if you have time, thanks.

[@KellyCactus]

Thanks for the clear and concise information.

[@krnlg]

Dual channel timers can be useful with combi boilers if they allow control over preheating. My boiler is a good example; it can preheat a small amount of water stored inside the boiler itself so that the water is hot much faster when a tap is turned on - but that means more gas usage as it will gradually lose heat into the room and then heat itself back up again. That can be controlled by a seperate channel of the timer so that when nobody is in the house it doesn't still keep its reservoir of water heated up. If, for any reason, somebody is in the house anyway while it is "off", it still turns on and heats the water just without the speed of having a pre-heated portion to go straight to the tap.

[@warrengray610]

Hi john, the permanent live also allows the pump to run on! Good interesting subject matter always found boiler wiring interesting, actually inspired my now prolific hobby electronics Best regards Warren

[@hectorheath9742]

Thanks, John, pretty straight forward but nice and reassuring that I'm doing things correctly nontheless. I briefly read somewhere that some controllers can adjust the boiler output to optimise efficiency. More research required on my part I guess.

[@humbletraveler2004]

Very good information about wiring. Thanks so much

[@fixoheat895]

Outstanding, as usual.

[@generalb.m.s15]

Thank you John !

[@EquilibriaHealth]

Great information. Clear and very well explained. Thank you.

[@ewb69]

superb explanation, thank you.

[@IrishHitman79]

Excellent Vid John.

[@ollieb9875]

Thanks! That looks like a fancy gamer's chair you've got there 😁😋

[@Bari_Khan_CEng_CMarEng]

Excellent guidance, much appreciated

[@TheMachopecho]

explained very well thanks john

[@miyanm338]

Such an excellent video I must say on the subject by John gr8 stuff

[@vegantheonlyway8692]

Brilliant explanation

[@loafersheffield]

Fairly comprehensive description of wiring configurations. Ty JW. However! The location of the thermostat or stat/prog is an important consideration too. It must not be placed directly above a heat source or it may well get.... confused(?) I have attended numerous properties where the stat is placed upon a wall in either in direct sunlight or above a radiator, or in the case where the prog/stat is portable (battery-wireless option)...and not permanently fixed to the wall has been placed upon a mantel piece above a gas fire. A "t" stat, controls the operation of the boiler on heat mode. Whilst it may be cozy and nostalgic to watch the fireplace fluttering away... the boiler will not heat the rest of the house as it primarilly determines whether the gas valve opens and fires up. Also, as a wall stat dictates when a boiler fires on either time and/or ambient localised heat controls, I'd still recommend the addition of thermostatic radiator valves. Why would one illuminate a room when one is not inside. Turn off the light. Crank down the TRV's in unused rooms, close the door to the room.

[@robertdunsmore]

Excellent help, many thanks.

[@MattNation1]

excellent video - very helpful!

[@rolikaseventysix]

Amazing explanation! Thanks a lot!

[@mikmik7033]

Excellent video john as usual top video i have a glow worm with 2 vf contacts

[@jeddyman4135]

You explained everything so welll, 26 minutes well spent for me. Hats off to you pal💯💯💯

[@zakovbbronchi5393]

thank you for your great tutorials ...great im still learning...thank you

[@tahirmahmood1854]

Thank you JW. TC.

[@train4905]

Brilliant john as allways sir thankyou

[@claw1770]

Great video, and very helpful.

[@johnscott8592]

Hi john thank you for the comprehensive description. I have a question though. What should I do with the wire to the standard mechanical clock control on the boiler its self?

[@hetanhawke1695]

thanks Mr .

[@sbusweb]

+John Ward I've seen older non-electronic, mechanical thermostats that simply have 2 contacts only (no neutral)! that ARE the old 'twisty-dial' style. I get the impression they use a mechanical mechanism to provide the needed "hysteresis" (not turning on and off repeatedly at threshold). I think we have an older honeywell thermostat of that variety that (appears) to work fine. An obvious (to me) solution if you for some reason want to use mains-output 3-terminal thermostat, or the hive dual-channel "mains" output, is to connect this N/SL output across a 230v relay coil, and put the secondary of the relay across the boilers' volt-free-contacts ... WHERE/how to safely locate the relay and how to crimp/solder/whatever its' terminals correctly is another matter.

[@jwflame]

The relay is certainly an option, and is usually what's done where there is an existing combi boiler without mains switching, and additional heating zones and/or a hot water cylinder are installed.

[@colincurd3901]

Thank you take care regards colin

[@Unklemikestube]

Thanks John, a very comprehensive explanation and easy to follow 👍🏻

[@kevinmcneill7056]

Brilliant thank you

[@williamcattrell8869]

Very good Advice

[@RoofRack2]

What a well made video.

[@kylebishop6233]

Congratulations, upon achieving 60,000+ Subscribers.

[@davyogi9796]

Very very helpful thanks

[@tomflynn78]

Very Informative

[@brendanwills702]

great info thanks

[@siywintertv6842]

I need you guys haha i was installing a steam boiler right now and its crazy difficult when i only has a very low knowledge on it..,

[@oneclickworkshop9853]

Amazing thank you very much

[@stevenmatthews673]

Thank you 🙂👍

[@musicbydavidyoungs]

Good video, thanks.

[@SproutyPottedPlant]

Always wondered how my boiler's wireless thermostat worked or could have a different type of thermostat! Now I know. I imagined it being some weird custom cable that only Glow worm and British Gas could connect to their own thermostats.

[@lucindaburton11]

Hi John, another extremely helpful video! Is there any possibility you could do a video on thermostatic wiring to a Combi Boiler that has 2 UFH thermostats and 1 or 2 Radiator thermostats? I understand that NEST can support systems that have dual heating in the property, such as radiators on one floor and UFH on another floor - but I am yet to find any helpful videos on how this particular system would be set up. Many Thanks!

[@PanPuchacki]

Thanks for the video. I'll attempt to wire a Drayton Wiser smart thermostat to a Potterton Gold 28 boiler. Seems pretty straightforward until I open the control panel on the boiler.

[@propman1823]

What a legend!

[@edlount1]

thanks John, really appreciate what your doing and how easy you explain things.. :)

[@rossmurdoch1886]

Excellent explanation John thanks Can you tell me if you have experienced issues powering a cylinder thermostat with an RCBO?

[@stephen9553]

John how do you wire for a heat pump , thermostat and a water tank and what’s the best program?

[@train4905]

Awsome john😊

[@SaltwaterC]

The rumour that the 3 wire thermostat (L, N, LS) is dead may be a bit exaggerated. Had one of those old looking twisty-dial things, but it is in fact an electronic thermostat, Drayton RTS1, on a fairly new build i.e 2013. Even more, its replacement basically went into the same mounting wallplate, albeit with a link between the L and 1 terminals - referred as "industry standard wallplate" in the Drayton literature. That replacement is a Drayton Wiser Heat Hub with all the latest bells and whistles, but on the boiler side of things it is a bog standard switched line on terminal 3 no matter how fancy the tech surrounding the relay actually is. The only alternative provided on the hub is OpenTherm. My boiler was released more than a decade ago (the product, not the actual unit in my house), although still sold as Worcester's top of the line product. This could make it a tad old. However, the Wiser system is recent and they haven't seen a market for providing more than these couple of connectivity options for the boiler.

[@Triune3]

Hi John, can you make a video for Combi with zone valves? Thanks in advance

[@clivebrooks8207]

Hi John, great video but you are mistaken about using combination boilers in large premises. I have a combi boiler fitted in my 5 bedroom house with two bathrooms and have found it works extremely well. It can easily supply two showers at the same time and at mains pressure. I had to fit a pump to get sufficient pressure to have a shower with the old system. I never have to worry about someone having a bath and using up all the stored hot water. The only slight negative is that you cannot have the heating on at the same time as running hot water but that rarely causes a problem. Also it halved my gas bill although the old boiler was well past its best.

[@Deegius]

Love the videos, John. We have here thermostats on each radiator, seems to work well but we need a new boiler as the one we have got damaged. Does this matter, there is no electrical thermostat only a timer.

[@jaxmar88]

Thermostatic radiator valves (TRV's) dont actually electrically turn the heating off, you need a room thermostat also but remove theTRV from the radiator in the room where you fit it.

[@alanhudson6607]

Hi John. Thank you so much for the video, really explains things well. I've an old rotary Honeywell stat wired to a Gloworm Combi boiler in a Volt Free setup. I've bought a 'wired' Wifi stat that requires a constant live obviously. Can I power the stat from a 3amp fused plug into a nearby mains socket and just connect the 'volt free' connection to the existing wiring straight to the boiler?

[@jwflame]

Theoretically yes, as the switched contacts won't be connected to the power supply for the receiver. However it would be far better to connect it to the same supply as the boiler, and as the receiver unit should be installed next to the boiler there really shouldn't be any reason to use a separate plug.

[@pukesmells]

13:37 for the Nest Wiring

[@garethmairs4897]

Hi John thanks for the info, is there a pump on the central heating system or is it built into the boiler and if there is, is it supplied off the switched live side

[@jwflame]

For combination boilers the pump is inside the boiler. For others, it can be in the boiler or a separate item. Either connected to switched line, or more usually connected to the boiler itself so the boiler controls the pump.

[@MrWolze]

Amazing video , well explained ..... Have you done a video on opentherm?

[@jwflame]

No. For the connection of the wires it's just 2 of them to the 2 terminals, and it doesn't matter which way they are connected either. Most of the deal with Opentherm is the configuration of the thermostat or other device, which is unfortunately a journey into incompatibility and disaster, as although it's an open standard, certain manufacturers have decided to implement it in ways which only work properly with their own equipment.

[@MarcioFenelon]

Very informative, thank you. Still really uncomfortable with my setup. I have a combi boiler junkers euroline zw23 and want to fit a generic thermostat bought at Leroy Merlin called Garza Top Power. It seems pretty straight forward, boiler LR/Ls to thermo COM/NO, and boiler Ls/Ns to thermo L/N. Makes sense?

[@jwflame]

Yes, 2 wires for the switch contact and 2 for the power.

[@bbcode4]

Ufh- 2 manifolds with heatmeiser 8rf wirening centres + rf switch. Is there any chance to pair 2 wirening centres to 1 rf dual chanel switch?

[@philalthorpe4864]

Great video Im after a bit of advice. I was replacing my motherinlaws stat which is a battery digi one. At the wall are only two wires red and black. I replaced it with a wireless stat which has 4 terminals. 4 live 3 neutral 2 volt free in 1 volt free out. When the two wire are connected to 3 and 4 it powers up unit but no switching the heating on or off. How do I wire it up to operate heating. The instructions say about bridging a connection but are very sketchy to say the least

[@jwflame]

If the battery stat worked with just those two wires, then those are the wires for volt free in / volt free out. You will need additional wires for the L&N supply. However a wireless receiver isn't intended to be installed where the old thermostat was - it's installed next to the boiler which will have all of the required connections, and the wireless thermostat is located wherever you want it.

[@dlewis129]

Hi John Any chance you can do a video on the overpriced nest system. I can find a good one anywhere and yours are always top draw. The ones I found show the heating side but not really the hot water side Ie how to connect into the cylinder stat. Cheers

[@stewartharrod1706]

Could you do one for a neomitis thermostat Awesome video

[@booveedoo]

Excellent, well informed video sir. Question. I have a Worcester boiler 30i and Hive single receiver. Looks like I bridge L and 1 on the Hive plate as it is zero voltage contact. Is this correct? Thanks

[@jwflame]

Yes, and then 3 is the switched 230V AC output to the boiler. Most Worcester boilers use 230V switching, however you must check the instructions for your specific boiler, as there are many different models and revisions.

[@feliceiafolla9002]

I am looking to replace an older type 3 wire mains thermostat that you describe (limited to minimum setting of 14 degrees C), with one that is capable of being set to 5 degree C ( just to keep pipes from freezing). Can anyone identify a manufacturer of such a thermostat?

[@dotvisionsys]

Hi John, I have Baxi 40 Titanium Combi Boiler and two S Valves for each floors heating. I am struggling to wire it with the hive multizone system. two separate receivers for each floor thermostats. I will be very grateful if you can do a quick drawing for me.

[@ranat5526]

My T.V is also a box!

[@paulhoward4981]

Thank you, after watching the video I decided not to fit the Optimum Vibe RF Programer because the instruction was not that clear to me. It looks like you connect 230v to 3 different terminals, switch on and blow something up. Considering there are 5 wires from the boiler and 3 wires from the mains, even if you cut off the earth wires or use a connector block for earth, is it unreasonable to expect a wiring diagram that shows exactly where the other 6 wires go into the receiver unit? I may not be an electrician but I can connect a 13amp plug because I know where the wires go. My Honeywell CM927 instructions were quite clear. I didn't want to buy another CM927 because the digital screen on my one didn't last that long.

[@terry1128]

Hi, im trying to install the hive thermostat, but when i took off my old thermostat there was only three wires. Red Blue Yellow. Does this mean it is not suitable? The type of thermostat i have is the ones commonly found in uk homes, a while plastic box with a round dial . Appreciate any help.

[@jwflame]

Depends on what those wires are. If they are line, switched line and neutral then an single channel Hive can be fitted there , however the Hive receiver isn't intended to be installed where an old thermostat was - the receiver is normally installed next to the boiler and the thermostat located elsewhere.

[@akaashmohammed3680]

If I wired the L and N from the spur directly to the wireless receiver and then relayed to the boiler, would this also work?

[@akaashmohammed3680]

@Jules Moules Appreciate the advice!

[@parmbansal1]

Hi good morning just going through your video. I have purchased the Honeywell T4. would it be possible if I could send you a picture of my original wiring and if you could kindly advise. Existing wiring I currently have 3 wires coming out of boiler. If I could email you a picture or any other way of sending please

[@azeemmalik984]

Thanks John for the video. Actually I have ARISTON under sink water heater. The shoe is missing. I am using 13AMP switch/shoe. As I opened , I found 4 wires. Black, blue, brown and yellow. My place is 3 phase ground floor and single phase on the 1st floor. This 13amp shoe can take only 3 wires. Where the black wire will go. I wish I could send you a pic. Appreciate of you please advice. MAny thanks for the great video.

[@jwflame]

You will need to get the instructions for the heater - otherwise it's just guessing what the wires are for.

[@elviis67]

Hi John, I know it may sound dumb but I have a Honeywell BDR91 and am cofused as to where A&B would go to on the Hive Heating Programmer/Receiver would (A) go to Number 1 and (B) go to Number 3 as I cant tell because both wires are Black many Thanks

[@jwflame]

Doesn't matter, either way will work the same. The BDR and Hive are just a switch. When heat is required the two wires are connected together. When no heat, the wires are not connected.

[@elviis67]

@@jwflame Hi John, I would like to Thank you for your quick reply worked a treat Many Thanks

[@robertmcdermid7006]

Can I attach a standard 3 prong plug to my boiler as a temp solution to loss of power in the kitchen? And run it from an extension lead elsewhere?

[@jwflame]

Yes, and you could then run it from a generator or battery powered inverter if there is a total power failure.

[@robertmcdermid7006]

Thanks for such a prompt reply mate 👍

[@BigGoldenApple]

I have a question regarding connecting UFH thermostat connecting to current Combi boiler which has a RF Thermostat for Radiators. Can I have 2 x RF connectors connected to the boiler?

[@aliaalija4788]

hello sir i need your help for .. thermostat delta dore 6053038 connect to saunier duval gas boiler please guide me i can ?? thanks

[@melodic_breezy]

Hi John I have a hive single channel receiver to fit to a boiler which has never had a thermostat. The wiring diagram for the boiler(vokera vision 30c) says use contacts free of voltage but receiver says 230 switching power on the back. Should I be using 3 core flex from my receiver or 5 core flex and where in the boiler controls should I be connecting my flex to, if just 3 core flex then that’s simply just brown blue and earth but if 5 core needed where does black(1on receiver) and grey(3 on receiver) get connected to in the boiler? Any help would be much appreciated please, thank you.

[@jwflame]

Receiver connects to the M2 terminals in the boiler. Remove the link from M2, and put the 1 & 3 wires from the receiver in there instead. Do NOT connect 230V to the boiler terminals, doing so will damage it.

[@melodic_breezy]

John Ward brilliant thank you so much for the fast reply. And I take it it doesn’t matter what way round the 1 & 3 wires go into the m2 terminal block

[@jwflame]

No, doesn't matter. All the thermostat does is connect them together when heat is required.

[@abdulh63]

Hi John. In the example of a possible wireless room stat at 10.00, could you put a link from L to A. And then have B go back to the boiler as a switched line. I know you said it's a volt free contact it's just that I seen it like that somewhere. Will it work or will it destroy the PCB?.Thanks

[@jwflame]

Yes, that can be done - but only if the boiler uses 230V for the switched input. Volt free contacts can be used with any voltage, including 230V.

[@abdulh63]

@@jwflame Thank you John, much appreciated, One last question if I could, would doing this mean it the thermostat becomes mains voltage? Rather then volt free contact. Struggling to understand what makes it one over then other. Thanks again

[@jwflame]

@@abdulh63 Volt free just means it's not connected to anything inside the thermostat - you can connect any voltage to it. The other kind are permanently connected to voltage inside the thermostat, normally 230V, so with those they can only be used with 230V boiler and there is no other option. Same as having the link from L-A permanently built in to the thermostat.

[@abdulh63]

@@jwflame ah ha I think I've got it now! Thank you very much.

[@Swimfit998]

Hi John Could you please tell me what size wire i should have running to a combi logic boiler there is 2 different sizes on my wiring going through a room to get to the loft where the boiler is placed.

[@jwflame]

1.0mm² is plenty - the whole system is usually connected via a 3A fuse.

[@Swimfit998]

@@jwflame thanks John

[@fathahulalamansari6062]

I have an ideal isar h30 boiler my honeywell relay doesn't work so I have bought flomasta from screwfix will it work

[@garysunderland9844]

I have a ideal combi boiler with the nest learning stat that’s wired to terminals 2 and 3 for volt free switching in the heatlink but I’m asking anyone who knows if it’s possible to use the 5 and 6 terminals that has the live link to make them 240v and still keep 2 and 3 volt free. It’s just that I’ve added ufh and need switched power for the pump. I haven’t installed a zone valve as I only want one stat. Is this possible without blowing the unit?

[@markevans2040]

Hi I'm trying to work out how to wire my new Nest Thermostat e to my Vailaint Combi boiler. I currently have a Honeywell wireless thermostat and need to swap out the old Honeywell reciver for the nest e heat link. I've gone through the nest app instructions but I'm still struggling to identify the correct com on and no wires. The old reciver has Blue wire in N terminal, Brown in L terminal, then a small piece of black wire looped over to A terminal and finally a Grey wire connected to B terminal. I have been advised that in this case I need the Brown L wire and Grey B wire to connect to the heatlink but wanted to have a 2nd opinion as I thought the Brown L wire would fry the heatlink as it's battery powered. Any advice would be very much appreciated. Thank you

[@jwflame]

Brown and grey connect to the heatlink, blue is not required.

[@markevans2040]

@@jwflame thank you it's fitted and working well.

[@edgyVlogs]

I've got one of them smart thermostats, it has 4 contacts N, L, and then dry contact which one is straight line the other is bendy, out of wall i have 3 cables N, L, and Wake. Is there a way to wire it up for myself? Anyone knows?

[@edgyVlogs]

Nevermind i figured that out, had to bridge the L wire to A switch and add wake wire to the B, that worked. £26 smart thermostat with wifi that listens to what I say to alexa. That is quite impressive