pump overuns

[rhinosaw]

my old vented boiler defo doesn't have one, do all new boilers have one? would I be correct in thinking that a system boiler will have pump overrun built in but heat only will not necessarily or not definitely?

 

[stem]

The difference between a 'heat only' and a 'system' boiler is the way they are filled. The system boiler is fed directly from the cold mains, a heat only boiler is fed from a header tank. This has no bearing on whether a pump overrun is required or not.

The purpose of the overrun is to dissipate residual heat from the boilers heat exchanger when the controls shut the boiler down, so that it doesn't overheat and trip the safety overheat cutout. Whether one is required or not, varies from boiler to boiler, depending upon how much residual heat the boilers heat exchanger has. Those with a cast iron heat exchanger will have more than a stainless steel one for example. Some models that have the facility run the pump for a period of time, others have a temperature probe and keep it running until the water has cooled sufficiently.

 

[Mottie]

I thought a system boiler had all the bits of the system inside the boiler - pump, expansion vessel etc? I have a heat only boiler (external pump and expansion vessel) and it’s filled directly from the cold mains.

 

[shambolic]

The difference between a 'heat only' and a 'system' boiler is the way they are filled. The system boiler is fed directly from the cold mains, a heat only boiler is fed from a header tank. This has no bearing on whether a pump overrun is required or not.

The purpose of the overrun is to dissipate residual heat from the boilers heat exchanger when the controls shut the boiler down, so that it doesn't overheat and trip the safety overheat cutout. Whether one is required or not, varies from boiler to boiler, depending upon how much residual heat the boilers heat exchanger has. Those with a cast iron heat exchanger will have more than a stainless steel one for example. Some models that have the facility run the pump for a period of time, others have a temperature probe and keep it running until the water has cooled sufficiently.

Wrong.
Heat only can also be sealed system.
Pump external expansion vessel external.
It’s that the components are all in the system boiler, pump, expansion vessel.
Excluding zone valves which are outside boiler on both types.

 

[stem]

Sorry, I thought that was what I said, it was what I meant to say. A Heat Only boiler can of course have an expansion vessel but, it is not inside the case, sorry for any confusion.

 

[transam]

Some heat only boilers do not require a pump over run

Viessmann is optional

Baxi eco blue and its derivatives pump over run is not required

Intergas probably does not ??

 

[Dan Robinson]

Intergas probably does not

Depends on the situation.

 

[shambolic]

Ideal does not but I have seen some issues with 30kw on poorly designed systems overheating occasionally as the heat stays in the boiler.

 

[ianmcd]

Ideal does not but I have seen some issues with 30kw on poorly designed systems overheating occasionally as the heat stays in the boiler.

remember the suprima 120, still see a few and the problems they had with overheating because they didnt have a pump over run, my own personal view is that all modern boilers should have a pump over run as they are getting smaller in size but the load is increasing, the heat has to go somewhere