Hot water priority with multizone

[Ben565]

I thought I'd start a new thread for this rather than continuing to hijack someone elses.

I can't see how to configure Hot water priority with multizone. Currently I have an S-Plan system with two zone valves. One for hot water and one for heating.

For Hot water priority Honeywell say I need two zone valves, one for hot water and one for heating (good I've already got this) each zone valve controlled by a BDR91. Great, got two of those as well.

Honeywell also say, BDR91 wireless relay box to control zone valve. And it turns out you can only bind it with one thermostat. Oh, so how does my HR92's and multizone work then ?

Well, you use one BDR91 to control the HW zone valve. And the 2nd one to control the boiler. And you fix the heating zone valve permanently open.


Riight, so how does hot water priority work then ?


It seems BDR91 as boiler control you can bind it with multizone HR92, but BDR91 as zone valve control you can only bind it with a single thermostat. So how are you meant to have multizone with hot water priority ?

[Ben565]

Ok just a thought

OpenTherm wireless bridge replaces BDR91 as boiler control. So... in my S Plan system

- R8810A OpenTherm bridge connected to boiler and bound to the Controller as boiler control
- BDR91 connected to HW zone valve and bound to the controller as HW valve
- BDR91 connected to the heating zone valve and bound to the controller as Heating Valve (or just leave this out altogether and fix open the heating zone valve)
- HR92 bound to the controller.

[Ben565]

I think I'm getting there and the penny is dropping (slowly)

OpenTherm wireless bridge replaces BDR91 as boiler control. So... in my S Plan system

- R8810A OpenTherm bridge connected to boiler and bound to the Controller as boiler control (orange wire from zone valves not connected)
- BDR91 connected to HW zone valve and bound to the controller as HW valve
- BDR91 connected to the heating zone valve and bound to the controller as Heating Valve
- HR92 (s) bound to the controller.

That satisfies the requirement for two zone valves for Hot Water Priority (which only really works properly with opentherm apparently). And it also satisfies the requirements for multizone because R8810A has direct control of the boiler.


In Hot Water priority mode it shuts off the heating zone valve, opens the HW zone valve, and ramps the boiler up to heat the hot water. Thats why you need the Heating zone valve to prevent the high power/high flow temp overheating the radiators.

In normal heating mode, without any hot water demand. HR92 calls for heat, controller tells heating BDR91 to open the zone valve, and also fires the boiler up via OpenTherm.


Have I got it ?

[Richard]

I think I'm getting there and the penny is dropping (slowly)

OpenTherm wireless bridge replaces BDR91 as boiler control. So... in my S Plan system

- R8810A OpenTherm bridge connected to boiler and bound to the Controller as boiler control (orange wire from zone valves not connected)
- BDR91 connected to HW zone valve and bound to the controller as HW valve
- BDR91 connected to the heating zone valve and bound to the controller as Heating Valve
- HR92 (s) bound to the controller.

That satisfies the requirement for two zone valves for Hot Water Priority (which only really works properly with opentherm apparently). And it also satisfies the requirements for multizone because R8810A has direct control of the boiler.


In Hot Water priority mode it shuts off the heating zone valve, opens the HW zone valve, and ramps the boiler up to heat the hot water. Thats why you need the Heating zone valve to prevent the high power/high flow temp overheating the radiators.

In normal heating mode, without any hot water demand. HR92 calls for heat, controller tells heating BDR91 to open the zone valve, and also fires the boiler up via OpenTherm.


Have I got it ?

Yep, penny has dropped. Personally I would use X Plan instead of S Plan for this (NO Valve on heating rather than an NC valve) but this will work.

[Ben565]

Thanks for the confirmation, it took me a while but I got there. My plumber/installer was rather insistent on keeping the S-Plan system I already had, and retaining a heating zone valve. He's a bit old school, but a reliable and experienced.

He's fitted it now and seems to be working, with a few (hopefully) teething problems.

I did point him in your direction to buy the Evohome gear, but he bought it from his own trade source instead, sorry I did buy a DTS92E from you yesterday though, and amazingly arrived today ! super impressed.

[Richard]

Thanks for the confirmation, it took me a while but I got there. My plumber/installer was rather insistent on keeping the S-Plan system I already had, and retaining a heating zone valve. He's a bit old school, but a reliable and experienced.

He's fitted it now and seems to be working, with a few (hopefully) teething problems.

I did point him in your direction to buy the Evohome gear, but he bought it from his own trade source instead, sorry I did buy a DTS92E from you yesterday though, and amazingly arrived today ! super impressed.

Yeah shame that as I'd like to see the place he bought the items from support him with evohome like we do. Plus the trade outlet he used probably sold him older date code stock, so you won't get a 5 year warranty. Did the installer charge you 0% VAT? If not he should have if it was supply and fit.