Lukwarm rads - and only when the hot water is on

[slippyr4]

Basically, simplified, the programmer powers the valve motor only. When the valve moves over, it closes the microswitch inside the valve, and that microswitch completes the circuit with the boiler and pump.

If that switch isn't closing, then the pump and boiler will not run.

Obviously, the HW valve signal is "mixed" with the CH signal, so that either one of them can turn the boiler and pump on.

 

[robmorgan]

So, I should test the power to the valve with CH on. If there's power, I can assume the valve is faulty and replace it - correct?

Can the valve be replaced without having to drain the system?

 

[slippyr4]

So, I should test the power to the valve with CH on. If there's power, I can assume the valve is faulty and replace it - correct?

Can the valve be replaced without having to drain the system?

probably.

depending on how organised your wiring center is, you could swap the heads (and their corresponding wiring) over, and see if you have the reverse scenario (ie, no HW, working CH). That'd isolate the fault.

 

[chrishutt]

Did you study the S Plan circuit diagram and compare this with your circuit?

 

[robmorgan]

Yes - strangely, with CH and HW off, I get a 250V current between earth and the orange wires from the valves. How can that be?

 

[slippyr4]

Yes - strangely, with CH and HW off, I get a 250V current between earth and the orange wires from the valves. How can that be?

Volts are potential difference, Amps are current. And it's not wise to be using earch as a reference potential, use neutral instead.

But nevermind that... It's perfectly conceivable that grey and orange are wired the other way round. Typically, grey is live, and thus orange becomes switched live. But it could be backwards - which would not matter at all.

Test on the DHW valve - when DHW is off, one of (grey, orange) is live, the other is not. Then turn DHW on (make sure cylinder stat is calling for heat), this time both grey and orange should be live. Then test the CH valve- suspect that there will be no change between on and off.

Also, test the CH valve brown is 230V when there is CH demand (ie, when programmer and room stat both call).

report back with your findings.

 

[robmorgan]

With just HW on the grey wire is live. With just the CH on it's dead.

We don't have a room stat, but I can confirm that when the CHis on, the brown wire is live.

Dodgy valve then? I'm guessing it may well be the motor part, as I don't hear it wurr into action when I flick the CH switch on, whereas I do with the HW.

It appears the motor/switch assembly is screwed to the valve. Do we think I could just remove it and fit a new one without flooding the place?

Thanks again for all your help with this.

Rob

 

[slippyr4]

I agree, the motor sounds knackered.

The head of the valve should unscrew and come off, and this can be replaced (like for like) on it's own.

 

[chrishutt]

If the fault is merely the synchron motor, you can just replace that (£10 - BES) - it's quite easy to fit, if fiddly. All 230 volt motorised valves use the same synchron motor.

 

[robmorgan]

Excellent. I'll pop out tomorrow and see if I can get a new head/motor.

 

[ChrisR]

To get you warm, turn the HW thermostat (on the cylinder) right up , say to 70, and the thermostat (eg 1-6) on the boiler down to 1. Then put the CH valve lever in the hooky place which holds it in the MAN position.
Put the HW ON at the programmer.
The system will then try to make the HW hot, but fail to get hot enough because of the stat settings; meanwhile your rads will warm up. Thermostatic rad valves will still work but not the wall thermostat.

If there's a little bump on the top of the motorised valve head (only for Honeywell valves), it means you can remove the head (actuator) from the body to replace it without getting wet. The mechanics of the heads do wear out, but you can indeed just change the motor. (Synchron motor is sold widely, even in diy sheds). Sometimes it's easier to take the head off to get it into an easier position for you to fiddle with the two wires, then put the head back when done.
You can use an ordinary flat bladed screwdriver for the motor and head screws, but for the fairly recent ones a magnetic T15 Torx screwdriver works better.

If you change the motor with the head off, wiggle the lever to help seat the motor .

 

[robmorgan]

Hoorah! Replaced the motor and we're back in business!

Thanks all, cheesy as it may sound I couldn't have done it without you.

Cheers,

Rob