Frost Thermostat Installation - S plan, Y plan, Combi

Wiring for frost thermostats on S plan, Y plan and combination boiler heating systems. This uses two thermostats in series, the first senses air temperature and the second the temperature of the return heating pipe, so that if activated, the boiler only stays on long enough for the pipes to be heated, rather than heating the whole building.
Many boilers have internal frost protection, but that only senses temperature within the boiler, which may not be sufficient if the boiler is located in a warmer part of the building such as in an upstairs room.
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S Plan: • Central Heating Electr...
Y Plan: • Central Heating Electr...
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[@allsearpw3829]

Hi, a lot of installers should watch this video , just had the boiler changed and some installers have very little knowledge of wiring . Hung up my sparks tools a few years back , so needed to refresh a brain cell to see if it was still as I thought it was .🤔👍

[@buxvan]

Great video that finally got my brain to understand the wiring. Cheer.

[@adamlewisparker]

Always good to know how to wire up boiler control circuits. Thanks John for making time and sharing

[@rattlehead85]

Top Video as always JW. Cleared up a difference of interpretation a colleague had with me over how the frost and return thermostats work in tandem. 👌🏻

[@rossmurdoch1886]

Thanks John very well explained. Great clear graphics too. It can be daunting sorting out domestic heating systems when you're not familiar with all the options.

[@mattgreentree1689]

John, I’m a fan of your content. I have been a heating engineer for 28yrs and wire all my systems. It is common knowledge to professional heating engineers that you would always wire a frost stat and pipe stat in series in an exposed location. Also new condensing combination boilers in some instances now incorporate a frost protection.

[@sadiqdani9705]

Iv been up whole of this week, blaming wiser Drayton smart heating controls because the heating been coming on during the night randomly.. Luckily I was patient with wiser on phone with their resets etc. Now after watching your video I checked wall thermostat and it was set to 7° my boiler is in the garage. Haven't checked the return pipe yet. Amazing video even a goof like me understood that. I just hope it has cured the issue as I dread to hear the boiler come aswell as feeling hot at night as I'm in the room above it. Thank you so much

[@ukfreedivingbuddies]

Brilliant video, concise but with all the required detail.

[@muzikman2008]

Great stuff JW, i have seen these installed many times without the pipe stat fitted, in garages where the boiler is too. I always thought "shouldn't there be a stat to measure pipe heat?" lol now i know there should.I suppose there could be a short timed 10 mins on/off on the programmer for winter months at a push but...as our winters get milder in UK Frost stats seem to be fading away with the ozone layer ;-) great channel.

[@jitheshappukutty3616]

thanks John. The only video I rely for any information

[@markthomas3858]

Thank you John... Great explanation and schematics...

[@rubydoobstylie]

Thanks John, I'm about to upgrade my Y Plan to an S Plan (3 port valve keeps sticking) and also stick a Hive on it. I'd always wondered why there was no pipe stat next to the boiler (in the garage) next to the frost stat (probably cost cutting) Anyway I'm going to install a pipe stat while I'm at it. A perfect dummies guide.... which I probably need 👍😁

[@plumbertime]

It might have frost stat protection built in

[@colinmiles1052]

As usual very clear and concise. Thank you.

[@27forme2]

I thought a 3 port won't work unless it has wired to the grey wire

[@philchambers2554]

Thanks John very informative I am looking at this system to cover a external swimming pool system boiler fed just waiting on boiler type 👍

[@jarodec316]

Absolutely great job, thanks very much!

[@joeyoung177]

Great video, very well explained

[@simonmander4314]

Brilliant video

[@SPARKY400T]

Great video thanks for sharing the info

[@tinytonymaloney7832]

Spot on vid, thanks JW

[@dennislacroix5478]

Here in Canada we usually have forced air systems and I get why you'd want to keep the pipes warm but how does this help other pipes such as cold water taps or lines that go to taps in general if there is no water flowing in those parts? Does it just rely on the heat radiation inside wall cavities and such to keep other pipes from freezing? I would have thought it to just be easier to keep the air temp just above freezing.

[@EssKayTee1]

I have a Honeywell Sundial wiring centre. Where would I connect 1 from the frost stat and C on the pipe stat together?

[@foziebear]

well done

[@londontrada]

Surely you need to link the return to terminal 8 as well? Otherwise the hot water circuit would not warm up? 🤔

[@peto22]

Are those controls designed in 40's? Wouldn’t it be awesome if the boiler operated independently and kept the water at a constant set temperature and the heating circuit circulation was controlled steplessly by a three-way valve and the circulating water pump running continuously.

[@RainbowCharade]

Hi John, I am changing my froststat and found that the boiler switch does not shut off the live feed to it (voltage check). Switch does switch off boiler. Should I reconnect froststat live wire so it becomes switchable? - Or leave as permanently live even though it cant function anyway if/when boiler switch is set to off!?

[@alanshubrook4270]

Brilliant video! Can you tell me how I know if I have a SPLAN or Y PLAN heating system please.

[@jwflame]

Y plan has a single 3 port valve . S plan has 2 or more 2 port valves.

[@gbelectricks]

What’s the purpose of connecting the two stats in series? Could you not just get away with the pipe stat, as stand alone frost protection? Great video JW👍

[@jwflame]

Pipe thermostats do not sense air temperature. By the time a pipe and the water inside gets to near freezing, it's too late.

[@webbo73]

Hi John great video - on the diagram at 14:02, is it possible to use one single wire to connect position 1 on the frost stat to position C on the pipe stat? or does it have to be two wires going in to a terminal?

[@jwflame]

A single wire would work, all that's required is those two terminals are linked. However in reality you won't be using single wires as they would need to be installed in conduit, more likely is a 2 core flex to each of the thermostats.

[@lordpitnolen2196]

Great videos, JW. We have a Worcester Combi boiler but it is fitted outside against a totally exposed, external wall. I would imagine that, by default, it will already be fitted with a frost sensor? We have had this boiler for a few years and the only frost problem we had was an ice blockage of the '"condensate"(?) overflow into a small soakaway. This had been badly iinstalled. Any thoughts? Thanks.

[@loafersheffield]

I presume that the boiler is fitted in an attached outhouse or garage? Recent boiler plus legislation has addressed the issues re outside weather compensation sensors and upgrading condensate discharge diameters. . Soakaways are notorious, being buried in the ground, they are very susceptible to freezing. If it is run out on "overflow" that is 21.5mm tube, it will inevitable freeze up possibly even before it even reaches the ground level soakaway. You could try upgrading the tube to 40mm. A DIY job. Then wrapping additional lagging around the discharge pipe. You can even wrap a specifically designed heating coil around the pipe which is activated when the temperature drops, but this will not have any affect on the soakaway. The plumbers mantra "fill the kettle before I turn the water off" would apply. Pouring warm water over the pipe or soakaway will melt the ice obstruction, but it will again inevitably freeze during periods of sustained low outside temperatures. That is just a pain.

[@jwflame]

Some boilers have frost protection built in, others do not. Even for those that do, it will only work if the boiler itself gets to a low temperature, which won't cover situations where other parts of the building are colder than the boiler. All depends on the individual installation as to what is appropriate.

[@jwflame]

Some boilers have frost protection built in, others do not. Even for those that do, it will only work if the boiler itself gets to a low temperature, which won't cover situations where other parts of the building are colder than the boiler. All depends on the individual installation as to what is appropriate.

[@lordpitnolen2196]

Thank you. The boiler (an external model) is fitted completely exposed against gable wall. A relation has the same. The drainage system has been completely replaced with a T-branch should we have to add hot water. The soakaway has been enlarged. We have had no problems since this was completed.

[@stanslad7868]

I've lost count the amount of times I've had to explain to the plumber that we need a pipe stat as well, or the heating will stay on & bake the homeowner dry!

[@frimleyfrodo]

I grew up in a house in the 1970s that had a frost stat in the garage with the boiler. I knew when it was cold in the garage as I woke in the early hours in a bedroom that was so hot I could hardly breathe and it would remain like that until the garage temperature rose again. I can recall my father switching the spur off to try to cool the house down!

[@TheDickPuller]

I’ve lost count of the times I’ve wired CH controls for thick Sparks that couldn’t wire a torch!! Useless cunts are only good at pulling their wire!!

[@samwade6771]

Hi John can you do a video about SPD’s please?

[@jwflame]

Have already done 6 of those. kzbin.info/aero/PLVsHvs2Suqmo0GS6oa9l2kCN-A7QhIQe8

[@whitefields5595]

John, thanks for this. On a tangent, I am thinking of changing my current system from Y plan to S plan. The 3 port valve humms at night and is, I believe a compromise to save plumbing and valve costs. However, in terms of simplicity and controllability then S plan appears to be better. Do you have a view on this?

[@jwflame]

S plan is better in almost every way. The only benefit of Y was you only needed one valve, which saved a tiny amount on the installation cost- and that was decades ago when all systems only had a single heating zone and unvented cylinders were not something anyone had.

[@whitefields5595]

John Ward thanks for the fast response. Another ‘Lockdown Job’ coming up ....

[@whitefields5595]

@@jwflame John , just re-reading this. What is the relevance of unvented cylinders to S plan? thanks!

[@jwflame]

@@whitefields5595 Unvented cylinders require a valve which defaults to the closed position if power fails or the motor fails. Y plan defaults to hot water open. Unvented on Y plan requires the addition of another 2 port valve for the cylinder.

[@whitefields5595]

@@jwflame OK, got it. Thx again for a fast knowledgeable reponse

[@ranat5526]

Your a globie, fantastic info!

[@howieleem]

If the output of the frost stat and pipe stat in series goes to the white wire of the y valve, it will only send hot water down the heating pipework. But how do you wire it if you want the y valve to go to the mid position and send hot water down the heating and hot water pipework? Otherwise, wont the hot water pipework be vulnerable to frost?

[@jwflame]

Both white and grey would need to be switched, but that would have to be done via a relay. White energised from the frost stat, relay coil connected to the output of the frost stat and N, relay contact used to disconnect grey when energised. That arrangement isn't normally used as the boiler would have to heat up most of the hot water cylinder before the return temperature is high enough to open the pipe thermostat. Most HW cylinders are also located within the property that the radiators and pipes are in, so freezing of that isn't likely to occur.

[@howieleem]

@@jwflame thanks for the info. I will just make sure the hot water pipework in the garage is well insulated, and wire the frost stat to y valve for just the heating as you suggested. 🙂

[@sarkybugger5009]

Plan B: Add anti-freeze to your heating system, and fully drain your domestic water system, before buggering off to your Caribbean island for the winter. Anti-freeze is cheap.

[@millomweb]

No John, I wouldn't do it like that at all ! Room frost stat (located in unheated part of property containing water pipes) would only open all zone valves and start the pump. This would ensure all the heating system is at the same temperature. Pipe stat - positioned on the return from the longest circuit - and set to 2°C to fire the boiler. Putting the stat on the boiler return would find heat from the shortest circuit - likely a towel rail or even the cylinder coil. This would probably cause more heating than one would feel was necessary but at the point of turning the boiler off, the pump will keep running so the system water temperature will then even out over time. At the time point of heating, different sized zones will need different requirements and with the boiler off again, the pump will ensure the whole of all zones are at the same temperature and the pipe stat will keep that above 2°C. It must be remembered this will look after the heating system but not other household plumbing - notably tanks in the loft - which maybe ought to be on a heating zone of their own - along with any other water pipes like the rising main.

[@Stevie-m]

pmailkeey the problem with Jw method is you are not open the DHW valve running the risk of bursting the coil in water cylinder?

[@millomweb]

@@Stevie-m Precisely. At least the 3 port valve version could open both ports covering DHW & CH. BUT even with 2 2-port valves, room stat operates pump, pipe stat operates boiler - and zone valves not touched but left open manually - then everything heating-wise is covered !

[@robertmccully2792]

At a loss why anyone would have thermostat set at frost temp as you call it. Is energy really that expensive there? I am more concerned for heat loss reduction and keep at 50 USA. If your away from home for long periods drain the systems.

[@jwflame]

Yes, energy is expensive. Draining and refilling a central heating system is not a trivial thing. Draining it and leaving it empty for weeks will result in massive internal corrosion.

[@robertmccully2792]

@@jwflame I have a heat pump water heater on a recirc pump ( 100.00 with rebate). Very inexpensive, and all pipes are wrapped. 2600 sf house on electric heat on heat pump, is about on average 150 per month or less. Because i moved out of city proper i have no water bills or sewage bills. Those cost savings of no fees pay for all electric cost. WA State USA. Gas unleaded today drop to 2.09... No debt, everything paid for...