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. 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. 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. 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.

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. 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.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: 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. 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. 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. 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;

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. 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. 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 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. 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.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.