Evohome - Boiler overrun setting

[paulockenden]

Does anyone know what this setting actually does? In an S-plan or Y-plan configuration the Evohome system can't actually control the boiler overrun (it can't leave the pump running with the valve(s) shut), so any overrun will still be generated by the boiler itself, like with more traditional controls.

So what's the point of the setting?

P.

[top brake]

Does anyone know what this setting actually does? In an S-plan or Y-plan configuration the Evohome system can't actually control the boiler overrun (it can't leave the pump running with the valve(s) shut), so any overrun will still be generated by the boiler itself, like with more traditional controls.

So what's the point of the setting?

P.

Not available if system configured without boiler relay

It applies when you have Fig 4 application, zoned heating plus stored hot water

It allows the hot water zone valve to stay open a while after the hot water demand is satisfied (boiler relay turned off).

Allows the boiler to gradually shut down on its pump overrun without overheating by giving the heat somewhere to go to

Make sense?

Think of it like a cool down period after running your car at high speed before turning the engine off.

[paulockenden]

Yes, makes sense. But my system has no boiler relay configured yet the setting is still there. My boiler does its own overrun thing, and has a loop with an automatic bypass valve. So will this setting just be ignored?

P.

[top brake]

Yes, makes sense. But my system has no boiler relay configured yet the setting is still there. My boiler does its own overrun thing, and has a loop with an automatic bypass valve. So will this setting just be ignored?

P.

Indeed ignore

[Suncroft]

Hi,

I have a related question, I am installing Evohome as per Figure 4 on an oil fired heating system. I have a UFH loop with 2 port valve, a radiator loop with 2 port valve and a DHW loop with 2 port valve feeding an unvented tank. I plan for the HCC80R to power the UFH 2 port valve and UHF pump, to have a ATF500DHW kit control the DHW valve and to have a BDR91 act as boiler relay. The radiator loop valve will be left permanently open and all radiators fitted with HR92's.

My question relates to boiler overun and bypass valve. By current system boiler (Boulter Camray 5) does not use a pump over run feature which I think is because it is an oil boiler and the heat exchanger does not require one, also my system does not have a bypass valve. So if I dont have a pump overun then do I need to fit a bypass valve if setting up as per figure 4? Currently if the boiler is off, so to is the main system pump. However with a BDR91 controlling the boiler could there ever be a situation where the boiler and main pump are powered but all zone valves including DHW loop valve are closed?

Thanks!

[top brake]

You will still need a bypass valve to relieve excess pressure as the HR92 close down the TRV

If you don't the radiators may become noisy.

[Suncroft]

Thanks top break,

With regards to the bypass valve, all the 22mm (feed and return) from the boiler has been installed prior to the install of a large Hot Water tank which has all been boxed inside a purpose built cupboard so the only way to get access to the 22mm piping to fit a bypass would be to strip down the cupboard and/or remove the water tank, which is a big job. There is however an existing gate valve (currently closed) in 15mm piping between the feed and return which is accessable and could be swapped to a ABV. Should the bypass ideally be 22mm or would 15mm suffice? The feed to and from the boiler is 22mm and then the underfloor, heating and water circuits are in 15mm. Either way I will be getting a plumber to fit the bypass.

Thanks

[top brake]

Thanks top break,

With regards to the bypass valve, all the 22mm (feed and return) from the boiler has been installed prior to the install of a large Hot Water tank which has all been boxed inside a purpose built cupboard so the only way to get access to the 22mm piping to fit a bypass would be to strip down the cupboard and/or remove the water tank, which is a big job. There is however an existing gate valve (currently closed) in 15mm piping between the feed and return which is accessable and could be swapped to a ABV. Should the bypass ideally be 22mm or would 15mm suffice? The feed to and from the boiler is 22mm and then the underfloor, heating and water circuits are in 15mm. Either way I will be getting a plumber to fit the bypass.

Thanks

Will be fine fitted to existing 15mm bypass, flow rate very small to achieve the drop in pressure

[Suncroft]

Thanks for the advice, that should make life a lot easier, for my plumber anyway!

Thanks