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Brian, HVAC Technician
Category: HVAC
Satisfied Customers: 869
Experience:  OFTEC registered oil heating engineer and plumber.
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I have a Drayton LP722 which I think is tripping the main

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I have a Drayton LP722 which I think is tripping the main fusebox when a fuse is put into the heating system socket next to the LP722. This happens even if the CH Boiler is switched off which makes me suspect the LP722

Brian :

Hi my name isXXXXX could be the programmer but I would rule out the motorised valve first as this is more likely to fail than the LP722. the valve has 2 circuits one is only live when the thermostat calls for heat, this runs the motorised valve. the other circuit is always live and operates a micro switch that runs the boiler.


hi Brian. I have taken the lp722 off the wall, turned down the thermostat, switched off the boiler and put the fuse in and it still blows the ring main. What do you think I should try next?

Brian :

Hi I need you please, to go to the motorised valve and disconnect it from the wiring box just make sure you make a note of what colour wire goes where as I think this is your problem

Customer: Hi Brian. I have disconnected both valves( because I wasn't sure which was which). And with the timer pulled off from its contacts, the thermostat turned way down and the boiler switched off, it still trips the ringmain breaker. What's left? I did notice that after disconnecting the valves and inserting the fuse, there was a delay of a minute or so before the breaker tripped and so for that minute I thought we had found it. I'm puzzled now. Over to you
Brian :

How does your controller connect to the ring main breaker. Is it via a switched fused spur. if it is you will need to disconnect this and see if it trips. it sounds like you have a short in the wiring to the controller. Or from the ring main to the switched fused spur.

Customer: I'm afraid I don't understand. How can I tell? The fuse socket is next to the timer and all the wires are in the wall. All I know is that when I insert the fuse it trips the breaker and the computer and table lamps etc go off. Interestingly it doesn't blow the fuse. Sorry to sound so dumb but could you explain how I can test you theory.
Brian :

Hi no problem. Turn off the power at the main breaker and disconnect the wires leading to the controller from behind the fuse socket. it should only be live neutral earth.

Customer: Hi Brian. I found the fault after following your lead but it turned out to be a puddle of water in the connector box which is bolted to the under side of the boiler which is a Glow Worm boiler. I would not have thought of that without you suggestions.. I thought you would like to know for the next customer with a strange tripping fault. Many thanks and iI'll rate you excellent service. Thanks and goodbye.
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