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. 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. 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. 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. 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.

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; 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. 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. 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:There are 2 types of three port valves some have a mid position (Y Plan) and some don't (W Plan) the Y plan is more popular so suspect you have Y Plan. 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. 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. 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. 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. 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.

A DIYers tale.

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. However the plan shows one micro switch in the valve, in fact there are three, so meter readings were not as expected at the junction box. I was not sure it was the three port three position valve at fault, but as 4 pm approached I bought one anyway. 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. Digging so far indicates that if the controller calls for heating (with thermostat set above ambient temperature) nothing happens.

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. 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. 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. 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.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. 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. When the valve is not energised you get DHW (domestic hot water) when it is in mid position you get DHW and CH (central heating) and fully across you get CH only, so it is unlikely a valve fault will stop DHW from working.

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.