CH pump overrun

[akist]

On my very new system, when thermostat reaches set temperature, the CH valve closes, the boiler shuts down, and the CH pump keeps running for a few minutes more. With the valve now closed the pump is working against a shut valve. How is that meant to work? The bypass is before the pump and therefore I cannot see anywhere for the pumped water to go. Can the pump be harmed by working with a closed valve?

 

[cross thread]

Yes it can, plus it’s not cooling the boiler

 

[akist]

Yes it seems the installers did not do it right. The valve is shut, the pump works in overrun mode but does not achieve anything, and the heat inside the boiler rises from 45C to 60C. I then open the valve manually, and immediately the boiler temperature drops, as it should had it been installed correctly. When the flow was set to 80C the boiler reached 99.5C because of this!

 

[gas112]

bypass should be after pump and before valves can you stick a pic up ?

 

[akist]

bypass should be after pump and before valves can you stick a pic up ?

Here is a sketch I have made.

Also, even if the bypass is after the pump and before the shut off valve(s), the loop is tiny - why can't the valve remain open for the duration of the overrun?

 

[DP]

bypass should be after pump and before valves can you stick a pic up ?

Top 100 at work I assume
I wonder if the installer is able to pick his nose correctly

 

[gas112]

bypass in wrong place .
but i take it you have two port valves and not mid position 3 port

 

[akist]

bypass in wrong place .
but i take it you have two port valves and not mid position 3 port

Yes two 2port valves.

 

[Mister Banks]

Correct if I am wrong but isn't you new boiler a WB Greenstar 8000 which has an integral pump, why do you have an external pump as well.

 

[gas112]

Correct if I am wrong but isn't you new boiler a WB Greenstar 8000 which has an integral pump, why do you have an external pump as well.

there is 3 versions of 8000 2 have integral pump 1 doesnt

 

[akist]

Correct if I am wrong but isn't you new boiler a WB Greenstar 8000 which has an integral pump, why do you have an external pump as well.

It is a regular, not a system boiler.

 

[akist]

Top 100 at work I assume
I wonder if the installer is able to pick his nose correctly

Unfortunately, this is the majority of tradesmen I have met, regardless the discipline.

bypass in wrong place .
but i take it you have two port valves and not mid position 3 port

Yes, but even with the bypass AFTER the pump, I still do not like it, if the intention is to remove latent heat from the boiler, it is just too short a circuit, why can't the valve remain open for the "overrun" duration? Can it be wired so or is it too hard?

 

[stem]

why can't the valve remain open for the "overrun" duration? Can it be wired so or is it too hard?

It could be done with a relay or timer, and it's not rocket science. But, it would add another level of complication to the wiring, making it more difficult for some installers to understand and get right. Especially one that can't manage a simpler standard by-pass arrangement.

Then of course when the central heating is off, and the boiler is only heating the hot water cylinder, the same modification would be required to the HW motorised valve......

 

[DP]

Yes, but even with the bypass AFTER the pump, I still do not like it, if the intention is to remove latent heat from the boiler, it is just too short a circuit, why can't the valve remain open for the "overrun" duration? Can it be wired so or is it too hard?

Bypass is required to dispute residual heat in the boiler. Mechanical auto bypass is the easiest way to do it. What you want is possible but is the price going to be to your liking?

There are engineers out there who are on a different level and then there are those that think they are the best

 

[gas112]

the 8000 suggests having a minimum of 3 metres of pipework as a bypass it .