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. 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.

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: At the moment I am assuming that the valve is in the mid way position (otherwise we wouldn't be getting hot water from the tank and some heat from the radiators) and the strange behaviour of the heating is because it only works when the programmer for the hot water is on.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 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. 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? 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 .

For some reason later in the day, with the hot water off and the heating on, twiddling the thermostat does not cause the boiler to fire and the pump to run; I assume causing the pump to run is the critical test because the boiler usually fires a bit after the pump runs. That was why I came here and my misunderstanding has now been corrected thanks to John and flameport! Digging so far indicates that if the controller calls for heating (with thermostat set above ambient temperature) nothing happens. The system is a conventional gravity-fed system with gas condensing boiler, Lifestyle LP522 programmer, Drayton RTS1 room-stat, Honeywell tank-stat, Drayton MA1 MPV and ACL Lifestyle Wiring Centre.

Motorised Valve - Two Port

The default position of the valve is W, held there by the spring. Power can be applied to the white wire, grey wire or both white and grey. I turned off the power to the system and immediately the actuator returned to the relaxed, Water, position under spring pressure. 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; 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!) 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.

One side of the house, the radiators do get hot, Some of the other radiators don't, or at least take a long time (I've only recently put the hot water on constant). Pump is on flat out setting. This suggests that the radiators may not be balanced.I have a really weird problem with a Drayton MA1 mid-position valve and I can't find any reference to this specific problem. So, it seems as though everything is working normally until there is a demand for Heating only, when, once it is satisfied, the actuator remains in H. This is repeatable! The system has been working perfectly for 14 years until yesterday when the domestic hot water was cold. Boosted HW MPV stays in W. Boosted CH and MPV moves to H. Turn the boosts off and MPV remains in H and after a short time pump stops. If heating or water is called for the main valve opens and the 3 position valve moves to Heat or Water. If both are called for then the Mid position is selected which allows water to circulate to both.

However, turning off the system power causes the actuator to return immediately to the W, relaxed, position under spring pressure. Turn on the system power and everything works as it should, until the Heating-only demand is satisfied when the actuator remains in H. Now some heat is getting to the cold radiators. The new (compared to the others) double radiator is doing something I haven't encountered before. The rear part is heating up but the front part is staying cold. It doesn't have air in because I have bled it (amazingly after a long search I found a bleed screw) and it was full of water. With power applied to the white wire only, it will move to the mid position for hot water and heating. 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.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. Anyway having diagnosed this far I'm going to leave it with the central heating and the water heating on full time to see if I can get the temperature in the bungalow up to the expected level. 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. 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.