Hot water OK, no heating

[whydowebother]

Hi everyone - this is my first post so please excuse any crimes...

I've searched the forum, and tried a few things as a result but to no avail, please help:

I have a relatively new system, only about 5 years old. The boiler is a Glow Worm 38Hxi, it is a closed system with an expansion tank in the loft, and the system has a Grundfoss pump and a 2 Honeywell motorised valves, a room stat and a timer/controller box. The problem is that my hot water is OK, but the heating doesn't come on. The first thing I checked was the system pressure which had fallen to zero, I don't know why. I turned the valve and replenished it back to 1.5bar again and it has remained steady ever since. I have tried bleeding the rads and they are all full of water, no air. I changed the room stat for a brand new one, this didn't work either.

When I turn the hot-water onto 'continuous', the pump operates (when I change the pump speed switch I can hear the pump speed changing), the zone valve operates (checked by moving the sliding-lever to manual - no resistance) and the pipes get hot - all good. However, with the room stat set to max, when I turn the heating to 'continuous' nothing happens. The pump doesn't run, the zone valve doesn't move, and the rads don't get hot.

I tried the suggestion in the FAQ section - that is I turned the cylinder thermostat to 70, the boiler thermostat to 1 (or minimum in my case), and then turned the HW to 'continuous'. The pump ran and the inlet pipes to the rads got a bit warm - but I don't really understand the system well enough to know what I am looking for!

Please can you help - I've read through many of the threads on this forum but none of the remedies seemed to work for me.

Thanks very much

 

[lightning]

Faulty 2 port valve {c/h}

 

[45yearsagasman]

It could be something as simple as the synchron motor in the ch valve.

 

[whydowebother]

Thanks for your advice. Before I go and buy a new valve (or motor), is there a way I can tell if the valve is actually faulty? If I use the 'manual lever' on the valve, then I am pushing against some resistance, so the valve is closed. But with it manually pushed open, the CH still doesn't operate. Am I doing the right thing, or wasting my time with the manual lever?

Thanks

 

[PlumbGas]

take the cover off the valve head and if the head is fitted to the body with 2 screws not 4 you can remove the head no probs, when head is off there is a spindle which you can turn with pliers or some such tool, it won't turn much but if it turns and heating comes on it may have just been stuck. try this, if 4 screws don't remove head without isolating water

 

[PlumbGas]

 

[whydowebother]

Thanks Plumbgas - I removed the cover on the valve motor, then unscrewed the 2 screws and removed the motor (didn't get wet). The valve spindle turns easily so it wasn't stuck closed - however, moving the valve manually still doesn't bring the heating on. So with the room stat turned to max, heating set to 'continuous', and 2-way valve set open, the heating still doesn't come on at all.

Hot water still works fine.

I'm wondering if there might be a problem with my programmer/controller unit. Although the red indicator light comes on when I select heating to 'continuous', maybe that's all that happens? Maybe the unit does not actually switch on the heating? I think the unit is a Honeywell ST699 (judging from photos on google, although it might be a ST799, they look the same to me).

Is this possible - is this common? Is there any way of testing it, its pretty expensive to replace if its not actually the root of the problem?

Please does anybody have any more ideas?


Thanks a lot

 

[lightning]

Check your getting 240 volts at room stat

 

[whydowebother]

Mmmm...thanks for the 240V tip. I put a multimeter on the room stat and it indicates zero volts so looks like an electrical snag (or I'm placing the multimeter on the wrong terminals which is entirely possible - I'm putting the live on 1 and the neutral on 3 (Honeywell T6360)). Perhaps I should post a question in the electrical forum as well.

Thanks

WDWB

 

[mysteryman]

It is probably the Synchron motor in the CH valve.

Get the boiler and pump running with the DHW calling, and open the CH valve manually. This should give you CH. As a final check, look for 240 volts on the brown wire to the CH valve with the timer and room 'stat calling. If it is there, that confirms the faulty motor diagnosis - almost certainly - or it could be a wiring fault, in which case use the same logic. The pump and boiler are called on by either valves' end switch.

 

[whydowebother]

Thanks everyone - I followed your advice and the problem is now sorted. It was the synchron motor in the CH valve. Fitted a new one and the heating is now working again (just in time for the British summer...).