Well it was around Paul's comment on wind chill, i will be checking the office for bugs (Paul I'm looking at you) We have another cunning plan that the device is prepared for but needs additional weather data .... and now we get into confidentiality issues and project planning so I will stop there.
I don't have any radiators without HR92's anymore, so not in my situation no.
You're right though - if you did have a bypass radiator then at the end of a hot water reheat cycle in summer a small amount of latent heat from the boiler heat exchanger would be dumped into that cold bypass radiator, however that's a good thing for the boiler, and it would barely be enough to make the radiator luke warm and would only occur once at the end of each hot water reheat cycle. (The heating zone valve would stay closed until the hot water zone valve closed and the boiler stopped firing - then it would open when there was only latent heat remaining)
When I did have a bypass radiator it barely warmed at all from the heat dump due to the relatively high thermal mass of the radiator vs boiler heat exchanger.
Now that I have all HR92 controlled radiators I rely on a one minute hot water overrun to allow latent heat to dissipate at the end of the hot water reheat cycle.
Did you wire in hot water priority as well ? Or are all you radiators HR92 controlled to prevent radiators heating during hot water reheat ?
While that original idea of mine is better than just mechanically locking the heating zone valve open, (it allows full flow and also occasionally exercises the valve to stop seizing) I prefer the scheme I show in the circuit diagram above, as it is equivalent to what you are doing except when hot water reheating is enabled, at which point it reverts to normal TPI to prevent radiators going over temperature. Of course if you have hot water priority this isn't needed.
The above circuit is a further logical progression from the original idea to run the heating zone valve from the pump.
Last edited by DBMandrake; 3rd April 2020 at 10:51 PM.
All my rads have HR92s too, so I think a timer on my Heating MV would just be sufficient for when there’s an overrun from a heating demand - any pointers for what timer you used?
I use a 2 minute overrun on HW, plus the bypass rad in the garage for when there’s no heat demand for the CH.
I used an MRT16-REM:
https://www.cpelectronics.co.uk/ener...ches/mrt16-rem
It fits a regular protruding back box and has a blank front panel. A version with volt free contacts is availble but if you're just switching 240v AC the standard version is fine. The mode should be set to overrun mode and the delay can be configured anywhere from about 5 seconds to an hour, so it's quite versatile. Not sure how easy it will be to get hold of one in the current climate though!
My boiler is so old it didn't have any pump overrun at all - so this is my retrofit pump overrun. (An old boiler with no pump overrun really doesn't like TPI I discovered!)
Just got up this morning to find Bedroom Zone set to 35C.......and Living Room set to 19C, reading 15.5C, zone says calling for 100% heat, and yet Zone Valves are off and not pumping at boiler....
Roy.20200404_072012.jpg
Last edited by roydonaldson; 4th April 2020 at 09:32 AM.