HR92's on s plan

[AmaHaw]

Hi,

I have a system boiler and stored hot water cylinder, with HR92s on all rads (except towel rails). It's set up in s plan, but from what i can see from the installation guide pg 42 and pg46, and from what i can see from various forums, I think that this is incorrect? The heating however seems to work as required. There is the occasional 'boiler relay' fault but this seems to rectify itself. If it is incorrect, do i need to remedy as per pg46 of the manual with a bdr91 direct to the boiler or can it be left as is? Thanks.

[Richard]

If you have HR92's on all radiators, then we reconfigure the system so the heating system no longer has a motorised zone valve on the heating (as its simply not required and prone to failing if it is left in place).

This is in line with the guidance on page 46 of the new evohome installation guide (https://thesmartthermostatshop.co.uk/in ... 1649144370).

The only time we would keep the zone valve is if the system was on OpenTherm and we are using Hot Water Priority.

[pkeller]

I'm doing much the same, converting an S-Plan system with a stored hot water tank to a zoned system. I am fitting HR91s or HR92s to all the radiators and towel rails. Locking the central heating zone valve open as specified means (I think) that when all the radiators are off but the boiler fires to heat water for the tank, some hot water will still circulate through the radiator supply pipes . Have I understood this correctly? Is this a problem, and if so what needs to be done about it?

Thanks for any info.

[Richard]

(I think) that when all the radiators are off but the boiler fires to heat water for the tank, some hot water will still circulate through the radiator supply pipes . Have I understood this correctly? Is this a problem, and if so what needs to be done about it?

The only time central heating water would circulate around the heating circuit when DHW is on, would be if one of the radiators are calling for demand. If all HR92's are off, there will be no flow around the heating circuit, as heating pipes are piped in parallel.

[pkeller]

(I think) that when all the radiators are off but the boiler fires to heat water for the tank, some hot water will still circulate through the radiator supply pipes . Have I understood this correctly? Is this a problem, and if so what needs to be done about it?

The only time central heating water would circulate around the heating circuit when DHW is on, would be if one of the radiators are calling for demand. If all HR92's are off, there will be no flow around the heating circuit, as heating pipes are piped in parallel.

OK - this does fit in with my very basic knowledge about older systems needing a bypass radiator + a room thermostat (usually in the hallway - ugh!) when fitting dumb TRVs. This was how I originally understood things, but then I ran across comments like this https://www.pistonheads.com/gassing/top ... 158&i=1708 which started confusing me. Thanks for clearing things up!