DIY Doctor

Drayton MA1 Stuck in Central Heating Position

Postby PeteJackson » Mon Sep 23, 2019 9:24 am

Hi,
Bit of a problem with my hot water system which I have managed to narrow down (after looking at these helpful forums) to my Drayton MA1 being stuck in the ch position (at least I assume so as the central heating works but I get no hot water) - cannot move it manually either. Taking it off, I can move the valve manually (with a loud clunk!) but only anti-clockwise about 15 degrees (which confuses me as I thought there would be 3 viable positions). I turned the hot water on on the timer and looked at the bit that fits over the valve but it did not move. The motor certainly was reasonably warm. Any advice would be greatly appreciated!
Pete
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Postby ericmark » Mon Sep 23, 2019 8:24 pm

There are 2 types of three port valves some have a mid position (Y Plan) and some don't (W Plan) the Y plan is more popular so suspect you have Y Plan.

When the valve is not energised you get DHW (domestic hot water) when it is in mid position you get DHW and CH (central heating) and fully across you get CH only, so it is unlikely a valve fault will stop DHW from working.

The mid position is done by limiting current to motor and switching off/on as limit switch is activated, and full over by giving full current and the motor stalls so yes they get hot.

The normal problem is no CH only DHW as with DHW only the valve is not energised, the boiler is fed direct from the tank thermostat, so I would be looking at the tank thermostat, these have three wires, (four if there is an earth) it is wrong, but common to find the green/yellow is used for live supply so be careful. Both N/C and N/O terminals are used, N/O sends supply to boiler direct and N/C makes the valve go full over.

I would guess it has stuck.
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Postby PeteJackson » Tue Sep 24, 2019 8:29 am

So, I was totally wrong then! Moved the thermostat up and then back down again and now we have heating water. Some very dark magic going on there I think but thanks very much, you saved me a lot of hassle and money.
Pete
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Postby ericmark » Tue Sep 24, 2019 6:34 pm

Not by any chance RF linked? I have had that with cheap wireless thermostats, some thing has blocked signal or batteries low, and it will not send a repeat signal without turning dial up or down and return to original setting.

More expensive are fail save and repeat the signal, but cheap ones can stall.
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