No central heating, suspect 3 port valve

[MickBrown]

Customer has no central heating, hot water fine. When central heating selected with stat turned up 3 port valve does not motor to heating. No volts on orange wire, no volts on grey wire, 240 volts on white wire. My logic circuit says 3 port valve faulty.

 

[dontknowitall]

Would be my thoughts as well, but I'd check the temperature of the pipes to back up your theory.

 

[doitmyself]

Customer has no central heating, hot water fine. When central heating selected with stat turned up 3 port valve does not motor to heating. No volts on orange wire, no volts on grey wire, 240 volts on white wire. My logic circuit says 3 port valve faulty.

Are you talking about CH by itself or CH with HW?

If CH by itself, you should have 240V on the grey wire, from either HW OFF (timer) or HW stat Sat.

If CH with HW the orange wire should be live from the HW stat Call.

 

[MickBrown]

Thanks for the responses. The boiler and pump work when hot water selected, when central heating selected no boiler no pump and central heating pipes cold, 3 port valve stays on HW.

 

[doitmyself]

Thanks for the responses. The boiler and pump work when hot water selected, when central heating selected no boiler no pump and central heating pipes cold, 3 port valve stays on HW.

Sorry to repeat the question, but are you talking about CH on, alone, or CH and HW both running at the same time?

 

[MickBrown]

CH alone.

 

[doitmyself]

CH alone.

In that case you need to find why there is not 240V on the grey wire.

It comes from either the Programmer HW OFF terminal or from the Cylinder stat SAT terminal. So you need to check there are three wires to one terminal (grey, HW OFF, Sat).

What happens if you turn the HW stat down to min?

 

[MickBrown]

When I went back I checked the voltages again and there was 240 volts on the white and grey wires. Changed the valve and heating works but only when hot water selected as well. With only heating selcted on programer the heating did not work, there was still 240 volts on grey and white wires. Customer said they only ever had the programer on CH and HW so the heating only option may not have worked before.

 

[doitmyself]

Assuming it's a fully pumped system, did you check that the programmer was set to Pumped, not Gravity?

 

[MickBrown]

Follow up. Although the heating worked for a while it stopped again within a day. When the head was removed everything worked fine but when I put the head back on only the hot water worked. It appears the valve was sticking and sometimes it caused the motor to stop turning fully to make the switches to activate the pump and boiler. I changed the valve and all is okay now.

 

[RoryD]

Sounds like the powerhead has failed, however, just ensure that the cylinder stat is satisfied when calling for heat i.e. turn it right down. I've had a couple in the past where the cyl stat has kept the 3 port valve from turning the heat on (faulty cyl stat).