Worcester 8000 Series Converted To PDHW With Honeywell Home evohome | MWPHS.co.uk

In this video, Richard gives some details on how he converted a really badly controlled Worcester 8000 Regular boiler installation into an efficiently controlled system using two flow temperatures, very simply by using an inexpensive 10K Resistor and setting the correct boiler parameters.
Richard used Honeywell Home evohome in the video, however any controls that provide a switched live for heating and hot water could have been used.
Honeywell Home evohome was provided by The EVOHOME Shop - theevohomeshop...

[@solpcb]

Very nice 💯.. Shame your having to figure it all out Bosch would rather sell you EMS controls.. I've done PDHW on A Baxi Potterton Main heat only using an NTC. Parameters are easily accessible via the enabled OT bus.

[@MWPHS]

You wouldn’t believe the amount of people we’ve had contact us to tell us this isn’t possible. But yep, I prefer boilers with simple ways to enable PDHW, although the Baxi is really poor on its modulation ratio verses many boilers out there in a similar price bracket.

[@rubicula]

This looks as though a similar setup will hugely improve the efficiency of my Worcester 8000, which would be most welcome! Are there any installer menu items you need to configure to get PDHW functional, or is it just a case of just separately connecting the SL from the water and heating zone valves to the appropriate connections in the boiler? (And of course using a relay to prevent the heating zone valves activating when there is a call for hot water.)

[@MWPHS]

As far as we can tell, it is only the resistor we fitted that puts the boiler into PDHW mode. There are several parameters on these boilers and some need to be adjusted to get the most of the 8000 series boiler in your application.

[@mgbroadsterJ]

Why not just fit the Worcester mixer ? for PDHW ? The resister may take the boiler out of Waaranty .

[@MWPHS]

@@mgbroadsterJ because the customer had an evohome system and the MM100 wasn’t required. An NTC sensor is just a variable resistor so I don’t see why there would be a warranty issue (that was the least of this boilers worries).

[@mgbroadsterJ]

Some people use a normaly open 2port valve instead of relays. Where do you get the different resister ? How does it create two different temps without the Woŕcester mixer and if the mixer isn't needed ,why did they design it that way. Could I also use a Worcester wiring centre and not ha e to have somthing like evohome ?

[@MWPHS]

@@mgbroadsterJ I believe you are on my Delta T Hydronics group on Facebook? I did post about this a while ago on there. This boiler has now been removed and replaced with something more suitable for the property. But, yes Worcester make an EMS wiring centre and mixed circuit controller (we sell both items). You could use them, but was easier to do it my way with what we had at the time. The new boiler is on X Plan (NO and NC configuration). I will have to do a video when I have time as it is a plate loaded cylinder, so quite an interesting one. Thanks for your interest in this.

[@pghampton]

This is fascinating! So a just a 10ohm resistor will mean I can use my 8000 series (without the diverter kit) in PDHW mode?

[@MWPHS]

Correct. :)

[@pghampton]

@@MWPHS Wiring changes made - resistor added, hot water valve output wired to hot water live return on boiler & I now have two different temperatures! The boiler seems to be flowing to the cylinder at max temp (83 degrees or so) rather than the set hot water temp, but I can now reduce my radiator flow temp down to 50 degrees or maybe even less - some playing to do. The big advantage of this over the Worcester diverter kit is that I can keep the flow to the cylinder in 22mm pipe & make the most of the high output coil whereas the Worcester kit restricts to 15mm pipe. Also this modification is cheap as can be! I still need to modify the wiring or fit a normally open valve on the heating to make my system hot water priority, but having two flow temperatures is a massive step to a smarter usage of gas. Many many thanks!

[@MWPHS]

@@pghampton brilliant! Thanks for letting me know! 😎👍🏻

[@1000Mikey]

I'm going to be fitting a similar system with the same boiler and 3 heating zones. I will be using the ntc sensor for the cylinder. Have you used a normally closed relay to interrupt all of the browns on the heating 2 ports?

[@MWPHS]

Correct. The hot water receiver has a additional NC relay that when activated cuts the power to the zone valves. This is the relay I used - mwphs.co.uk/product/salus-relay-module-rm16a/

[@1000Mikey]

@@MWPHS thanks for getting back to me. So would I use 3 of those relays to interrupt each brown on the heating zones?

[@MWPHS]

@@1000Mikey that would work yes, although there are other ways.

[@1000Mikey]

@@MWPHS what other ways is there? I understand having a normally open 2 port if there's 1 heating zone but this wouldn't be ideal from multiple zones. Would it be possible to speak to you about this?

[@mgbroadsterJ]

Does it have the internal diverter fitted or can PDHW be done without it ?

[@MWPHS]

This boiler has PDHW without the internal diverter valve.

[@robotfridge]

Will this work on a worcester 4000

[@MWPHS]

Not tried it with a 4000 but can’t see why it won’t.