The orange wire from the second microswitch is there to provide a 'live' to operate the boiler when the 'central heating only' is selected (it takes over from the cylinder stat which has this function for 'hot water only' and 'hot water and heating' positions). The orange wire is connected to the white wire by the second microswitch, to provide this boiler control signal but it does not have any effect on the actual positioning of the valve.

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. 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.

Mid position valve problem.

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. 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; Just recently had to change my ACL Lifestyle mid position valve as a result of the rads getting hot when HW only was called for, which was due to old age, crap in the system and port A not fully shutting off. The new valve I fitted is a Drayton MA1, like for like swap on size and wire colours.

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. I had problems with my daughters old house, typical new baby so critical and a Sunday so had to find it parts required before shops closed at 4 pm. As an electrician I thought it would be easy, I found a wiring diagram for Y plan and tried to follow it. Is this something anyone has experienced or come across? If so, what’s the solution as I don’t want to fork out unnecessarily if it’s something simple to fix.I have tried looking at past threads but have been unable to find an answer to my dilemma, so I apologise if this question has been asked in past. 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: 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. 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.

Digging so far indicates that if the controller calls for heating (with thermostat set above ambient temperature) nothing happens. My son-in-law had tidied up the airing cupboard and had caught the leaver unlatching it. Result was when domestic hot water was required it motored open, but it did not open when central heating was required, however if the central heating was required then once the hot water was run, it would stay working until the thermostat turned it off again.

Swapping mid position valve

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. 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. 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.

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 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. 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.It worked and after it was all up and running we were able to work out what had happened. It would seem the fault was there before my daughter had bought the house, some one had latched the valve to mid position which resulted in radiators getting slightly warm in the summer, however daughter had not noticed this.