Grant Combi 90 Outdoor Boiler tripping LCD circuit and now the 3A spur fuse- help please?

[WhiteHart123]

Whenever any demands are made on the boiler through running the hot water or switching the heating on, the lcd trips immediately. We bled the pump yesterday and the system worked ok for a day and then all went off again. The burner will fire up after it has rested(cooled down?) but now after a lot of wasted time, the demands for water/heat are tripping the 3A fuse in the spur fuse box rather than on the lcd circuit.
Have bought a spare pump ready to install but not sure if the £120 is a necessary expense plus labour of course.
Grateful for thoughts. Grant team said they thought it would be the circulation pump if the burner is ok.

 

[oilhead]

Disconnect the pump, replace the fuse, switch power back on and see if the burner runs without tripping the fuse. If it does, problem sorted, change your pump. Remember to make pump wires safe when disconnected.

 

[WhiteHart123]

Thank you for the prompt reply. Not very competent/knowledgeable at all but can have a go tomorrow pre plumber arriving on Monday. How do we disconnect the pump? Do you mean electrically by undoing the black microswitch assembly. And then, if we can sort out disconnecting the pump, do you mean test it by making demands on the circuit through water and/or heating on? Sorry but real novices at this. Grateful for extra help!

 

[oilhead]

Disconnect the wires from the pump terminal box. Make the wires safe. Switch on the boiler. If you are uncertain about that, I would not like to think of you changing the pump, wait for your plumber.

 

[Agile]

I would always suggest disconnecting the pump and wiring it to a plug with a 3 A fuse and run that and see what the boiler does then.

Tony

 

[dilalio]

OP: can I also point out that it's your RCD that is tripping, not your LCD!
Maybe it's a good idea for you not to be tinkering with this problem!

 

[leakydave]

It should have a 5A fuse by the way.