CH on only when HW on!

4 Oct 2005
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United Kingdom
Hello There... I'm very new to this board, I only found it today!

I'm also a novice when it comes to plumbing / CH, so please by gentle!!

I hope someone can help me with my problem.(I've searched the site, but cannot find a solution)

My house has a boiler that serves both HW and CH via a fully pumped system (or at least the timer switch is wired for such!), so I can have HW only, CH only or HW+CH on at same time.

The HW has been running throughout summer with no probs, and a couple of days ago I thought about testing the CH as it was getting cold (it has been turned off for about 5 months).

Now, the CH won't work on it's own - the boiler does not come on and the radiators stay cold!
It does work if I switch on the HW as well, but the CH turns off once the HW has reached desired temp (I've got it set on the water tank for 60C). This is inconvenient to say the least!!!

(If I switch on just HW the radiators stay cold)

I've turned all radiator thermostats and the room thermostat up to full with no joy; I've also checked the wiring to the timer but it seems OK - I haven't delved any further!

Anyone have any ideas what the problem can be?

Many thanks for your time
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I'm sure someone more knowledgable than me will answer, but I have the same thing on my central heating system.

I found the instructions of the timer (it's a Honeywell, can't remember the model number) and it said on gravity systems you have to have the hot water on for the central heating to work, and normally the timer would be supplied with a sticker 'Hot Water + Central Heating' to go over the 'Central Heating' label :rolleyes:

Might not be the case with yours though.
Or better still check that the 3 port valve is not working correctly.
£1 each way stiff spindle at 10/1
£1 each way faulty motor at 8/1
£1 each way microswitch at 7/1 only 3 runners
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Or better still check that the 3 port valve is not working correctly.
£1 each way stiff spindle at 10/1
£1 each way faulty motor at 8/1
£1 each way microswitch at 7/1 only 3 runners

Looks like you've got yourself £10, Mandate!!

Stiff spindle - gave it a good pumping (cripes...sounds like a bad Carry On.. film!).

Job done!

CH now works a treat.

Thanks everyone for replies - I now have a happy & warm wife, 4yr old boy and 6mth old twins! Bliss - I'm off down pub!
Don't forget to send the winnings after deducting the stake money, remember it was an each way bet.
:rolleyes: :rolleyes: :rolleyes:
Hi, Mandate,

Sorry to be a pain - but before I go out and spend money, yet another question!

I said yesterday that i got the CH working again on the advice given in this forum - I was only partially correct!

The CH does not work again!!

Now what happens is this: I turn on the CH and it seems to come on. Then there is a "Click" sound and CH goes off. Observing the diverta valve shows that the "paddle" is in the correct place to begin with but as soon as CH is switched on the "paddle" moves out of position and turns off CH!!!

Is this a duff motor?

If so, it looks easy enough to replace, but how much is one and where can I get one? (I live in Southend area of Essex if that helps!!)

If not - what can I do & how much will it cost to repair?

Thanks and apologies for more questions!!
tollanarama is online now Edit/Delete Message
You may need to look at some of my recent posts where this problem is covered.
However the basics of valve is there are 3 positions and the valve is spring loaded. When CH only is demanded the valve moves against the spring to the full extent and in doing so it operates 2 micro switches. one of which supplies power to the boiler/pump.
So what happens is either the valve is not moving over enough or if it is then the microswitch is not working. You can check for voltage on the orange wire of the valve and you should be able to hear or observe the valve moving.
When you demand HW along with CH the valve moves to the mid position. But the microswitch (which may be faulty) does not play an active role (power come from different route) so the CH works. Now for the second but. How long will it be before HW is satisfied? not that long I say (having a bath might increase the time). the cylinder being insulated it will not lose much heat so as soon as HW satisfied valve moves back to CH only and back to the problem.
Take the motorhead off the spindle again and try HW only followed by HW/CH followed by CH only and back to HW/CH and watch the locating slot turn about 45 degrees each time. Also check the voltage on orange wire at each stage.
If the spindle is free theres only valve movment and microswitch left.
I replaced the whole motorhead for £38 although I knew the problem was the microswitch.
A replacement motor is around £10. try B & Q warehouse.
where on earth is Southend?
:rolleyes: :rolleyes: :rolleyes:

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