Central heating doesn't work but hot water does

I'm not a boiler expert (hopefully you'll get someone along here who is) but when I've had this on 2 combi boilers on renovations in the past, both times its been a failed diverter valve which isn't switching over from HW to CH. in both cases the value needed replaced. not sure what you mean by the "2 port valve" but like I said im not an expert

 

Listen to what your CH two-port valve tells you. When you turn up your room stat (with your timer also 'on'), the valve should whirrr for a a couple of seconds and also produce a distinctive 'click' as the microswitch is triggered.

It's that MS that actually then turns on the boiler.

When you turn the room stat back down, the same should happen - a similarish whirrrr and click.

So, have a listen

If it goes whirrrr but no 'click', try clumping the valve body repeatedly with summat soft but firm - enough to give it a shock but not damage it... See what happens.

 

Ah, that narrows it down...

Ok, it's either that the timer ain't sending an 'on' voltage to the room 'stat, or the room 'stat ain't sending that 'on' voltage on to the valve, or the valve is kaput.

Do you have (a) a volt meter or other mains tester, and (b) a working brain?

If so, you can do some testing.

The first would be to open the wiring centre - the white box all the valve and 'stat wires go to - and identify the wire that operates the valve (I'll have to look it up...)

I think it's the brown of the valve that becomes 'live' when the timer and 'stat call for heat.

 

I'd personally like to check that there's power getting to the valve motor first, before going to the hassle of replacing it.

It should be a simple test, and I think is worth doing rather than resorting to diagnosing a fault by replacing components on a test and see basis.

Having said that, the chances are that it's indeed the valve motor.

If so, you'll then have the option of chust replacing the motorhead, leaving the actual valve body in place so no need to drain down.

Meanwhile, we don't really know if it's the valve, 'stat or timer - or a wire in between.

A mains tester screwdriver is an ok alternative to a voltmeter, and may even be preferable in this sort of case - it has some advantages like being instant and only having to place it on one terminal.

So your call whether to hold out for a multimeter.

 

That's pretty much it!

You won't be able to test the neutral except with a multimeter set at AC Voltage - testing across the blue and grey should show 240. You can therefore assume that the neutral is ok.

Then, as you say, check for the brown going live when the timer and 'stat are both calling for heat.

That particular vale does have a removable head, so you won;t have to drain down your system - assuming the valve part is in good condition. You might also be very lucky and find that the cable going to it actually plugs in and isn't hard-wired - do you know if this is the case with yours? How lucky would that be?!

Anyhoo, let us know what you find.

 

Coooooooooool


And hopefully soon hoooooooooot

 

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