Twin pump central heating help

[Steve746]

Hi everyone

I've got an issue with my central heating system in that suddenly after years of no problems, the radiators have started getting warm when they aren't supposed to. Essentially when the hot water is on but the heating is off, the water is still circulating around the radiators.

I've got an old Thorn boiler, there was an SMC controller on the wall next to it, but I replaced this this several years ago by a more modern Sunvic controller and a junction box.

I've had a good old google, and was surprised to not be able to easily find the heating system I have. This house is the only one I've had with central heating, so I didn't know any better! What I seem to have is two pumps, one for the hot water and one for the central heating. The pipe comes up from the boiler to a tee, and one direction goes to the red hot water pump and tank and the other goes to the black central heating pump and radiators.

From what I have found it looks as though at one time there maybe was an SMC control pump, but at some point this was changed to what I have now? The pump is coming on when its supposed to, so is the idea that its meant to stop water going round when its off? Would this mean it needs replacing? More to the point is this setup normal?

Any help would be much appreciated!

Thanks

 

[The Teach]

More to the point is this setup normal?

systems vary,some are complicated some basic some diy but its all down to cost .

As long as the black pump is not rotating,the fault will be a defective spring operated non return valve possibly adjacent to the radiator pump. There again some systems require the user to manually turn off all the radiators at the trv or wheel head valve.

The hot water pump could be run on a minimum speed with the boiler thermostat turned to a lower setting but that depends on other system requirements.worth a try

A control upgrade to single pump and motorised valves could be considered and possibly a new boiler,its your call