Good day,
I have been experiencing a problem with my domestic heating system. There are occasions when the system makes noises that seem to indicate that water is circulating. These occasions however occur most often late at night when the system is not due to be working. The noises occur despite the timer being at a time when it is at "off" for both hot water and heating. The gas boiler is not alight at these times.
The noises come from my airing cupboard tha6t houses a Megaflow style water tank, a lot of pipework and what I believe is the circulation pump (manufactured by Grundfos). its difficult to tell but the unexplained noises seem to be coming mainly from the Grundfos unit. During these occasions, the unit is very warm / hot to the touch.
I have consulted plumbers and heating engineers about this problem but so far no one has been able to diagnose what is happening.
I would be very grateful for any advice.

Chris, January 2021

The first thing to check would be the zone valve/s
They look like little silver boxes, fitted where two or three pipes meet up and will have a wire running to it. Take a screwdriver and unscrew the metal cover to expose the mechanism, then unscrew the two diagonal screws that hold this mechanism to the brass valve it’s attached to. You may have one or two of these zone valves, so check one at a time if you have two. Remember there are live wires under the metal cover, so be careful. Pull this mechanism off the brass valve and you may find it clicks back to it’s off position and the pump will then stop. It this happens, you will need to replace the sticking valve body that this mechanism was attached to.

Rupert, January 2021