3 Port Power Head Trouble?

[scubapete]

Another one...

The heating has decided to stop working. It worked OK last week.

The CH thermostat switches on, but the boiler doesn't fire. If I turn the HW on at the same time, the boiler fires and both water and radiators are heated until the HW thermostat turns off and everything stops even through the CH thermostat is still demanding heat.

I've had the power head off completely and done some tests from the FAQ 17. Here's a picture:

Untitled

• scubapete
• 17 Sep 2013
• 1

When the CH only is on the motor turns, but stops when switch A clicks on. The motor doesn't turn far enough to hit switch B. There is 0.00V across the orange wire.

If I jab a screwdriver in there to force switch B, there is 240V on the orange wire and the boiler fires.

However, after a few minutes the motor starts 'hunting' and switch A starts to click on and off.

If I lock the lever in the 'manual' position, it makes no difference.

If I pull the lever as far as it goes (past the 'manual' lock) then switch B clicks and the boiler fires. If I let go, the motor relaxes until only switch A is on.

Any ideas?

The system is a fairly conventional gravity-fed, gas fired boiler with HW cylinder, F+E tanks and cold water header tank.

I have a wireless thermostat and so when it's CH season the CH setting on the programmer is set to Continuous as the heating schedule is totally controlled by the wireless thermostat.

Cheers.

 

[MANDATE]

TH71 has the same problem. just answered it a minute ago

 

[scubapete]

Cheers Mandate, you'd also posted on a couple of other threads today that were helpful.

I've checked the voltages on grey and white wires also to make sure the problem isn't elsewhere.

But, the actuator is stopping at the mid position and not going on to the CH only position.

So, from your other comments it's got to be the micro switches -> new powerhead unit.

I wonder if this glut of actuator posts is normal or just because everyone is switching on their heating again...

 

[D_Hailsham]

If I turn the HW on at the same time, the boiler fires and both water and radiators are heated until the HW thermostat turns off and everything stops even through the CH thermostat is still demanding heat.

Find the terminal with the valve grey wire connected. There should be two more wires to this terminal: one from the programmer HW OFF, the other from the cylinder stat. The above description suggests that the wire from HW OFF is missing.

I've had the power head off completely and done some tests from the FAQ 17.

Did you check that you can turn the valve shaft easily by hand (less than a quarter turn)?