CH expansion pump over

[cc47]

Hi

I'm installing a DIY heat pump alongside an existing vented CH/HW system & I'm getting a small pump over from the expansion tank.
I've raised the expansion pipe as far as I can in the roof space & the circulating pump is set to its lowest setting but still get a small pump over.

Can anyone see why I can't use an inline DBV in the expansion pipe, which will only open when the pressure in the heat pump circuit exceeds say 0.5 bar (ie on heating up)?

I looked for pressure relief valves but these all seem to be for unvented systems in the 3 - 5 bar range; too high for my system.

 

[ChrisR]

DBV

EH?

What's the boiler?
You may be able to seal it, otherwise no you can't add strange valves. A combined feed and vent may be possible.

If the plumbing were right you wouldn't get any pump-over. See the FAQs?