Removed heating MV now hot water won't come on!

24 Nov 2013
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United Kingdom

< Traditional vented system with CW and HW tanks, and 2 motorized valves for CH and HW>

So as we're in summer, I was annoyed to find the CH partially on. I think what happened was that a drayton za5 had yet again failed and was stuck open. So not having much time midweek and not really needing the heating on at all at the moment, I thought I'd remove the head of the valve from the circuit box completely.

I did that and of course that broke the hot water 8-( . When I turn the HW on at the programmer and ensure call for HW is on at cylinder stat, the HW motorised valve opens and I can then hear the relay switch click but the pump doesn't start like it should do. (It was definitely working 5 minutes before I had the daft idea of removing the heating MV).

Is that the normal behaviour when removing one valve from a two MV system? Whilst I'm waiting for the new za5, is there anything I can do to get diagnose why the HW MV isn't turning the pump on?

Thanks a lot in advance for any help.
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You can test the microswitch electrically.

But if you don't get any further after removing the CH head you can select CH and let that head turn on the boiler.

Ever thought of changing to a Honeywell or one of the copies?

As both of the motorised valves have a microswitch that is connected to the boiler / pump, when you removed the wires from the central heating motorised valve, you may have disturbed the wiring from the other, particularly if they were in the same terminals. I would start with checking them. (Grey & orange wires) Are the screws tight? is the insulation trapped instead of the conductor? It would be a coincidence (but not impossible) that the microswitch in the hot water valve failed at the exact same time as you removed the central heating wiring.

You say that "the pump doesn't start" when the hot water is calling for heat. Does the boiler fire up? Is the boiler itself switched to on? With some installations, the microswitches start the pump and the boiler together, with others the microswitches just control the boiler and then boiler controls the pump separately.
Thanks both for your answers.

The pump and boiler are powered together but I think I found out what I did wrong - I removed the wrong (the CH) MV so no wonder the faulty HW one was still faulty! That sort of stupid mistake is typcial for me unfortunately...

I've since replaced the HW one with the good CH one and left the CH valve manually closed until I get a new one.

However, I think the CH valve itself is faulty because I can't close it - I mean can easily rotate the pin clockwise or put an old head on the top in a closed position, but it lets water through - so much that the rads get hot unless I turn down the TRVs. Sods law is it is right at the back of the airing cupboard on a 28mm pipe with loads of pipes in the way 8-(.

I would like to get rid of the Draytons since they seem to fail reliably every 18 months. One outstanding follow-up question is if I replace the faulty 28mm valve with a like for like (since very little space to put something bigger or smaller than existing there) would say a Honeywell actuator fit it? Or maybe I should buy the honeywell valve if they are the same length as the Draytons? Was also wondering about sunvic.

I was also thinking maybe if I remove the valve, I could remove any obstruction preventing it from closing?
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I find that generally Honeywell motorised valves have a long life. My mother still has the original Honeywell installed in her bungalow controlling the central heating from when it was built in 1980. To be fair, it doesn't have a microswitch which can be the cause of failures, so I had to wire a relay to it in 1985 to provide this function when it was converted to an 'S' plan.

Also, I have three Honeywell's in my home that are all at least 8 years old, after replacing the original Landis and Gyr valves that only lasted 4 or 5 years. (Two of them leaked, and the microswitch failed on the third)

If there is an obstruction in your valve, you maybe able to remove it, but I think it more likely that the valve is faulty.
So preferred option is a honeywell. Do you know if the 28mm version is the same length (or close to) as the existing faulty drayton?

I'm only asking because I don't mind doing a bit of pipework, but with pleanty of 28mm, the 22mm shower pump pipes, plus oversized cylinder and with this actuator being at the back of the cupboard, it would take (me at least) a _lot_ longer to fit if I have to re-solder a ton of painted 28mm and 22mm joints that have been there since the 1980s! The valve is jammed in between two ancient soldered connections.

If it is just a case of dismantling what I need to get a pair of spanners on the valve and whatever else might need removing to get a bit of leverage but if the Honeywell is much bigger or smaller I think I'd need to redo a lot of the pipework which (if I'm doing it) would probably triple the amount of time I spend doing it !

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