Grundfos pump on continuous and boiler fires intermittently when controls off.

[Zandana]

Hi all, appreciate a little help on this one. I have an oil boiler (thermecon) in kitchen and hot water tank (megaflo) upstairs in airing cupboard. In airing cupboard there is a grundfos pump running continuously, and two zone valves: metal Honeywell and plastic covered Drayton.

Boiler is firing intermittently despite the controls for hot water and heating off. System otherwise seems to be functioning perfectly normally apart from this and the pump running 24/7.

Any ideas?

 

[hertsboilers]

Zone valve fault to give constant switched live to boiler and pump

 

[Zandana]

Any way to tell for sure? Have a multi meter but not sure where to start...

When I manually override the Honeywell to open (with commands off) there is resistance and it springs back slowly after. Can hear water moving around and pump goes quiet when I do this. Not sure if that info adds anything

 

[J_N30]

There are electrical checks you can do but I don’t want to be held responsible for you electrocuting yourself!

Best thing to do is feel for a hot pipe after the valves. You’ll then know which of opening when it shouldn’t. Very common for an actuator to supply 240 when it shouldn’t.

 

[dilalio]

Stuck microswitch on a 2port valve, either CH or DHW. Identify wires from the microswitch(es) and see if they are sending 240v to pump and boiler.

References available online but proceed with caution.