I’ll be calling in the local firm for a service and a bit of troubleshooting on my central heating in the next week or so.

However, it’s always good to have some kind of background inkling of what’s going on beforehand.

Boiler kicks in fine for hot water, doesn’t do it for CH on its own, only when HW is running too. There are two motorised two port valves, and the obvious choice of fault is the heating valve, which makes a low hum but seems to do bugger all else when you select the CH.

Anyone had experience of this kind of thing – is it a straight swap out of the whole valve normally or a fettle to free it up?

Or have I missed something else? There have been some mysterious intermittent pressure drops at the boiler with no obvious leak or overflow to explain them.

Assuming it’s the motorized valve that has failed, it’s not a massive job to replace it. Still cost you a few bob but I can’t remember what it cost me when I had that issue.

Take the motor off the valve, (should just be a few of nuts/bolts) and see if it moves without being attached to the valve when you fire the CH up. You can twist the valve stem with a pair of pliers to see if that’s stiff while you are at it, then at least you know if it’s the motor or valve.

Both are easy DIY jobs really, the hardest bit being re-filling the system if you have to drain it.

Edit – and if you want to take the valve out, you really do want to drain it! (just in case, sorry if that’s a bit obvious)

Motorised valves usually have a manual over-ride anyway. Look for the small lever that sticks out the side of the casing, it usually has a detente to it can be left open.

It could be that the thermostat that controls the valve has failed. (check operation of the valve as noted above)

Fortunately the installer has left me some isolating valves above and below the motorised valves so I’m wondering whether a swap out is within my (limited) capabilities. Really don’t want to drain down.

Yep, will go and check the motor. Cheers.

drain down isnt a big issue. really it isnt …. provided you know where you mains tap is.

really dont suggest doing it without draining down

the valves on mine were sticky and a sharp tap to them with a hammer sorted them out for that actuation – but when they shut at full temp they jammed again.

depends on the layout of your system but i was advised against fixing my valves open to heat the tank as i risked a overheating the water and it all heading out the overflow up so i wouldn tempted to do that as a cheap fix.

threw the whole lot out in the end(15 years old at least) and put a combi in.

*i am not a pro just ran into problems with a system that no one would touch and all wanted to condemn…… so i did the right thing in the end 😉

Make sure it’s not an electrical problem by checking that the valve is getting power when the timer/thermostat/controller switches.

The motor appears to be getting power – you can hear the tiny hum and vibration when you turn on the heating from the controller. No movement on its spindle, just a load of black gunk around it. So still the prime suspect.

Do these valves default to open when you remove the motor?

Do these valves default to open when you remove the motor?

No. The motor drives both ways.

If you have isolating valves either side of the motorised one, still be careful. Turn off the mains water first, isolate the motorised valve and when taking out the valve release the nuts carefully, don’t just whiz them off. As soon as you get the dribble of water that remains in the valve/pipework stop and let that drain. If it doesn’t stop one of the isolation valves may be passing. Tighten the motorised valve nuts again reconsider your options.

Had similar to this recently; could only get hot water when CH was on.
Local plumbers from old school boys to flash, all the gear/no idea bloke in next village were stumped.

Eventually found http://www.midlandboilercare.co.uk/ who knew exactly the cause over the phone and came and fixed it pretty quick – nice chaps.

Had something similar a while back.

The power cable routing to the motorised valve meant that the cable was always under pressure, especially when the airing cupboard was full. This led to the cable connections to the pcb in the valve motor housing coming adrift, and as they are (apparently) soldered, not screwed connections, a new motor was needed.

Found one on ebay for way less than list price and had the local plumber fit it.

With the heating “on” and the stat turned up, wiggle the cable around and see what happens.

Cheers

I’m pretty sure now it’s the motor in the valve – I can get it to work, but only intermittently, so I’ll swap a new one in and see what happens.