Upstairs rads on when CH off and HW on

[gunnag]

I have a problem with upstairs radiators being on when only the hot water is on.

My system is configured as follows:-
- Boiler Potterton Prima F
- Potterton EP202 controller allows independent control of CH & HW
- Room thermostat downstairs British gas RS1, 3 wired red, blue & yellow
- Hot Water Cylinder thermostat Potterton PTT 100 3 wires connected orange, brown & white
- A pump is located in the airing cupboard before the three port valve
- there is a tank in the loft to fill the CH & HW as needed
- a 3 way valve is fitted with a Sunvic SDMV2304 motorized valve

I have recently fitted TRV's to the entire system except towel rail and rad in room with thermostat.

Despite the TRV's I still get hot rads, now some of the downstairs rads get hot as the TRV on them is fully open whilst upstairs are on a low setting.

I have noted that when the HW is on and CH off, the 3 port valve still seems to allow some flow to the rads as port A. Could it be the valve is leaking and some flow is leaking through to the rads? This valve was changed about 5 years ago because of a similar problem, maybe there is dirt in the system?

Alternately, perhaps the Sunvic SDMV2304 motorized valve is wired incorrectly.

All info welcome.

 

[Armo74]

Doubt it's a wiring issue if it is a new problem.

Either the valve is letting by or it is reverse circulation caused by a piping issue.

You need to check if the heating return is piped in after the hotwater return.

 

[Terry lambert]

If nothing has changed on your pipe configuration and it is a recent problem, I would say your motorised valve is faulty

 

[gunnag]

Thanks for the reply, I checked for a heating return pipe but cant see one, much of the pluming is hidden.

This may be an issue with the valve letting by. This morning with all the pipes cold, I turned the HW on. I felt the boiler feed pipe become hot and the pipe from the 3 way valve to the HW tank become hot. Additionally, the pipe from the 3 way valve to the CH became hot.

So I guess either the 3 way valve is letting by or the motor is incorrectly mounted? I noticed the "D" on the actuator was facing port B for HW.

 

[gunnag]

Last weekend I removed the 3 port valve and checked its operation. Turns out it was leaking internally and letting hot water past the valve to the rads when it was supposed to go to the HW cylinder.

I have now swapped out the 3 way valve for a new one I picked up in Wickes for only £40 as the packaging was damaged. The new valve is made by Siemens, whether its any good or not remains to be seen.

I believe the old valve was damaged by sludge and sediment in the system so have decided on the the following course of action:-
- add sludge remover to system and run through rads and HW system for a few days. I may isolate all radiators except one, which should flush out the remaining sludge in the open rad, this will be repeated for each rad.
- I have bought a magnaclene pro and intend to fit this immediately before the 3 port valve
- I will be adding inhibitor to suppress the formation of further sludge

Hopefully this approach will solve future problems.