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 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. 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. 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.

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 . 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. 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.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.

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. 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. 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. 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. The problem with the cold shower remains a mystery, appears to be a one-off and it has not happened again.

With power applied to the white wire only, it will move to the mid position for hot water and heating. 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? When HW and CH are calling for heat at the same time, the valve moves to the mid position. The boiler and pump are still powered directly from the cylinder stat.

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. 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!) Last night my partner heard a very strange buzzing whiring noise coming from what i now know is the "mid position actuator" . 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. 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.At the moment, there is nothing wrong with the system, thank goodness. It was a case of putting two and two together and coming up with five. The water was very cool when I showered and so I advanced the timer to heat it up. The boiler was working fine as I had the heating on at the same time. 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. 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. Digging so far indicates that if the controller calls for heating (with thermostat set above ambient temperature) nothing happens. 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 system has been working perfectly for 14 years until yesterday when the domestic hot water was cold. 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. As I said, when I turn the water on, the actuator does move to either the mid or W position depending on whether there is demand for Heating as well. In that respect it all works perfectly.

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: 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 have a really weird problem with a Drayton MA1 mid-position valve and I can't find any reference to this specific problem.