Location of control valves - Florw or return.

[Michael Chare]

In a fully pumped domestic heating system, does it matter whether the control valves are sited in the flow or return pipes?

Are there any advantages in using the flow pipe or disadvantages of using the return.

I see that some Honeywell control valves specifically state that they are not suitable for siting in the return. Why might this be?

(I'm thinking of converting to a fully pumped system, if I put the control valves in the flow I will have to install additional pipework for the overflow - something I would like to avoid.)

[Andrew Gabriel]

I guess the valve paddle may not close the ports with enough force to prevent the pump pushing it open if fitted in the return.

[Christian McArdle]

They are traditionally put in the flow. However, the return provides the advantage that the temperature is lower, providing, perhaps, better reliability.

I can't actually think of a reason that you mustn't put in the return. However, if you are thinking of installing S-Plan in a system that doesn't have a boiler suitable for sealed pressurised operation (even if you are keeping the vented operation), then be careful that there is an unbroken path to the boiler return from the fill pipe. This will necessitate the use of a manual bypass valve, rather than an automatic. Old type boilers rely on a supply of quenching water into the boiler return to prevent them running dry when they start producing steam. There won't be enough pressure to open an automatic bypass when just gravity feeding the boiler with cold water.

Christian.