Potterton Promax Heating Coming On With The Hot Water

A common complaint at the end of winter is that the heating keeps coming on with the hot water. I immediately went to the airing cupboard to look at the motorised valve with the hot water set to be on. I felt the lever which in the photo below is on the underside of the valve and could feel that it moved freely from left to right. When the valve is in the hot water only position there should be little or no movement on the lever without force.

It could either be that the motor inside the valve has seized, their is a fault with the electrics causing the valve to open or that the paddle is stuck in the wrong position. I checked the electrics to ensure that there was not 240 volts at the white or grey wires to the motorised valve, which there was not.

In the case of this older Honeywell 3-port valve the power head is not removable from the body. If you try to remove it from the body it actually opens up the body itself and you will have water coming out. If the problem is with the body you can actually strip them down and grease it up after draining the system but it's usually better just to replace the valve which I did in this case. To tell the difference between the two types of Honeywell valves you need to look for the dimple on the silver case which can be clearly seen in the photo on the right circled in red. This is the same for both 2-port and 3-port motorised valve head made by Honeywell.

Disclaimer: The works described in this blog are a record of work undertaken and should not be taken as guaranteed to solve your problem. Work should only be carried out by persons qualified and competent to do so.