What type of non-return valve for a 22mm heating return pipe?

[Jock Spanners]

Good Morning All,
I've just got a customer with a heating fault from their system boiler. When they turned off their heating for the summer they found the upstairs rads were still getting warm when they heated hot water. The boiler is in the corner of the kichen with all the pipework in the tight angle of the loft above. The return from the primary is linked to the return from the upstairs heating circuit by a tee so hot water is flowing across the tee to the rads instead of down and back to the boiler. It's going to be really difficult separating and soldering the existing pipes so I thought I could put a non-return/single check/double check valve on the heating return to stop the primary flowing into. Perhaps I'm misguided but I've always avoided these these - I'm always suspicious of their reliability. Could anyone recommend one that won't impair the return?
Many thanks,
Jock

 

[Deleted member 120897]

We have to fit them on Intergas boilers (shared heat exchanger) that are situated on the lower floor of a house, as when preheat is on or the hot water is ran it circulates up the flow/return.

We fit a single check valve, which is what Intergas technical advise.

Regarding separating, could you use compression, rather than solder?

 

[ShaunCorbs]

I’ve used the screwfix single check before now no complaints