One year ago (almost to the day) the Drayton MA1 mid-position actuator was replaced (4 years old) on my central heating system as it wasn't operating correctly. It was replaced with another MA1 and the problem was solved. However, I have just switched on my central heating for the first time this year and find that I always get CH with HW even when the CH timer is off. I looked at the MA1 and can see that the valve position is in the middle (HW+CH). If I unsnap the actuator from the valve I can turn the valve manually. I then tried the following with the MA1 removed: Very frustrating and don't know what else to do with the damn things other than to have a different make and model installed. I don't do it myself. I get a professional to do it - thank god I have an all-singing-all-dancing central heating insurance cover to deal with it. The manual lever only moves the valve to the mid position, and is useful when filling or bleeding the system to make sure that all water paths are open. It will flop around when the valve is powered to the mid position or beyond - this is normal.

It seems to have two functions; an open/close switch and a three position switch for Heat Mid and Water. I assume that the logic is roughly; The MPV actuator is a BGMVSP-23. The control and thermostat is a Hive system. Boiler is a Worcester Greenstar Ri. System is gravity fed open vented system, tanks in the loft and HW cylinder in airing cupboard. formatting link When there is a HW demand but not a CH demand, the valve is un-powered and sits in the HW position. The boiler and pump are powered directly from the cylinder stat.

Edit: I've just done some more investigating this morning. The problem of the pump continuing to run last night, doesn't appear to occur when I try it now. I unplugged the MPV and it caused the pump to switch off and the valve return to its default W. I have looked up the model and found it to be a "drayton mid position actuator MA1" and wanted to know what i need to do to replace it . I do know they have a circuit board and very flimsy, but normally reliable, micro-switches but why would I want to go replacing the whole actuator, as you suggested in the first place, or even the circuit board as you now suggest, when the excellent descriptions of correct operation given by both 'Jonhmdc' and 'flameport' show that my actuator was working correctly all along and the only thing at fault was my understanding of its correct operation. The problem I am having though is even after the temperature set by thermostat has been reached, and after the scheduled CH OFF, my pump continues to operate, my radiators continue to heat and the temperature continues to increase.

With the head unit removed from the valve body, turning on the system and demanding Heating causes the actuator to move to the H position. Turning down the room stat satisfies the demand and the system shuts down the boiler and the pump but the actuator remains in the H position. Cycling the demand fires the boiler and pump but satisfying the demand with the room-stat has no effect on the actuator which stubbornly remains in H. I assume if the 3 way valve was working properly and the heating side wiring wasn't requesting heating then the 3 way valve would be set to Heat and the central heating wouldn't work. However although I heard the main valve move and watched the plastic lever move, I haven't heard anything from the 3 way valve and the plastic lever seems to be floating. So, am I trying to fix a problem that isn't there, (other than not having any hot water yesterday morning)? Perhaps I've never noticed the actuator staying in the H (or the last selected) position before.The best advice I got was that my system was working as it should and I am glad to say it is. From those who knew, I learned what it is that holds the MPV in the H position even when there is no demand for heating, the HW-OFF feed from the programmer. Given that, if the flow valve is permanently open and the 3 way switch is in the middle then water should always flow around the central heating. I have a really weird problem with a Drayton MA1 mid-position valve and I can't find any reference to this specific problem. That is, there is a shared (flow) valve which has to open to allow any water to flow, then a second 3 way valve which decides which way the water will flow. From what you say, does the actuator stay in the H position when the demand is satisfied when the timer is still on (as well as when the timer shuts off) and if so, what is keeping it 'actuated' there and thus stopping the spring pressure from returning it to the W position?

If the boiler doesn't run when there is *only* a CH demand, it indicates either that the valve hasn't moved all the way to the CH position or that the microswitch isn't working. As my MPV position indicator is 'hidden' from view, I had never realised that the MPV stayed in the last position demanded by the system and concluded, wrongly, that I had found the cause of the cold shower; assuming that the MPV had not moved when demanded. I had always thought that the MPV only moved to the H position when heating was demanded. Digging so far indicates that if the controller calls for heating (with thermostat set above ambient temperature) nothing happens. When there is a CH demand but no HW demand (tank stat satisfied or HW off at programmer) the valve moves to the CH position. A microswitch in the valve actuator switches a live supply to the orange wire - which then powers the boiler and pump.

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I was ready to go buy a new actuator as I believed this was the problem, however it appears to operate as described in the above discussion. At this point, demanding Hot Water causes the actuator to move to the W position and if the demand for Heating is still there, the actuator moves to the mid-position. (This is counter-intuitive to the problem of no hot water in the morning as when I test the system the actuator moves with hot-water demand even though it had not done so yesterday morning!)