C/H Question

It's called a bypass and is there so that at the point when both hot water and CH thermostats both want to stop the heat, the boiler will have a way to dump the excess heat. There will also be an arrangement in the boiler to keep the pump running for a few minutes.

Without this, the water in the boiler would tend to boil if the flow is suddenly stopped.

The valve should be left partly open to achieve this result.

.andy

To email, substitute .nospam with .gl

Thanks, I figured it was for something like this but there's no overrun on the pump. When the room and tank stats no longer demand heat the pump stops and so does the boiler, the boiler's downstairs and the pump's about 25 ft away horizontally upstairs.

Rgds

Andy R

It will also provide sufficient return flow when the TRVs are mostly off. If you're worried, then replace the gate valve with an automatic bypass valve.

Christian.

It also has a duel function, to keep the return temperature high to prevent condensation occurring in conventional boilers.

If you have had a boiler change the by-pass from the old system may still be there. If not a condensing boiler, keep it cracked open to keep the return temperature high.