Boiler Wont Fire When Asked for Heating

[r.rain]

Hello All

Ive just discovered that my Potterton boiler wont fire up when the thermostat (CM67) asks for heat. I have cranked the thermostat up to 30 degrees and still no joy. Hot water is fine and works as expected. I have recently removed a load of radiators upstair but wouldn't of thought that this would have anything to do with it and Ive also plumbed in a dual energy towel rad T'd off some existing pipework but again cant see that this should effect my boiler firing up. Any ideas?

TIA

Cheers

Richard

[r.rain]

Could this be a valve problem? just about to go look............

[Set Square]

Have you got a Y-Plan system - with a 3-port mid-position valve which directs the water to one or other or both circuits?

If so, when there is only a CH demand, it's a microswitch in the valve's actuator which switches the boiler and pump on. If the valve isn't motoring to the CH position, or if the micro-switch is duff, the boiler won't come on.

Similarly, if you have an S-Plan system with separate motorised valves for each circuit, you still need the valve to open before a set of contacts turns the boiler on.

Check the valve(s), and check whether the switched live feed to the boiler is *actually* live.

For Y-Plan or S-Plan wiring diagrams, see

and scroll down to the appropriate plan.

[Harry Bloomfield]

[e-mail] has brought this to us :

The valve actuator sticking most likely.

[r.rain]

Cheers SS. Sorry not enough info really on my original post, was in a rush to get out the door! It is a Y plan with a 3 port.

Well I had a look at the valve, nice shiny thing it is and found a lever at the side which says auto and manual. I pushed the level to manual and the boiler fired up. There was some resistance when moving the lever which I'm assuming was the balls or whatever they are moving and allowing the water to flow?

I then moved the lever back to auto and tried again, still no joy and the boiler doesn't fire.

I'm assuming from your post that the microswitch is fecked, but what does the auto and manual settings do? what will keeping it on manual do, does that provide water for both the CH system and the HW, so essentially when I have the CH on the HW will be on too basically both valves open and not allowing control via the motors?

Cheers

Richard

[techquest]

what motorised valve do you have?

Normaly the white wire is the CH side of the valve and is connected to the CH side of the programer. If the programmer is calling, i.e. on for CH and the room stat is calling , then the white wire should be at

240volts. You should see the lever on the valve, if working ok, move to the H side (Port B). If not then could be the valve, programmer or room stat at fault.

DHW side is the orange wire and you will get same conditions as above except on the orange wire and valve moves to W side (Port A).

Check with programmer on for DHW if valve moves DHW is working ok.

Check with programmer on for CH if valve moves CH side is ok.

Both DHW and CH on then valve moves to Mid position.

Check with your hand either side of the valve Port A and B to see if they are getting hot. If DHW is on then B will be hot. If CH is on then A will get hot.

Note in MID Position they could be equally hot.

Note, you can get a mechanical fault or electrical fault with these vales.

Regards

[Set Square]

More likely that the motor isn't working. Moving the lever to the 'manual' position moves the valve to the mid-way position where you get both CH and HW at the same time. If the motor is working it will be able to move the valve all the way to the CH-only position - which is what you need.

Take out the 2 screws which fix the actuator to the valve and lift it off. make sure that the valve spindle turns freely. If it does, the actuator is shot and needs to be repaired or replaced. You *can* buy replacement synchro motors - but it's far easier to replace the whole thing.

[Harry Bloomfield]

It happens that Set Square formulated :

I keep a ready repaired actuator alongside the working one, for a quick swap over. They do fail every few years.

Buy a new one, then work out what has failed on the old one and repair it as a standby. Motors can be had for around £15, microswitches for about £1.50 and complete new actuators £30 to £40.

[r.rain]

Yup motor it was, replaced and all OK

Cheers all

Richard

[Ian Cornish]

[Set Square]

In an earlier contribution to this discussion, Ian Cornish"