Boiler trips rcd when weather is wet and windy

[Pete]

Hello, For the last 2 or 3 months the RCD in our consumer unit has started to trip intermittently. All the sockets and boiler are on this circuit. The RCD only ever trips when it is wet and windy and always happens in the evening. After much unplugging and testing sockets I've finally traced the problem to the boiler. The last time the RCD tripped and I reset it I noticed that it stayed on for a few seconds, then when the boiler fired up it trips. So here's what I have done so far:

RCD tripped (Wet and windy weather outside) Turned boiler off and room thermostat to zero Reset RCD - it stayed up Turned on boiler - RCD still OK Turned room thermostat up to fire up boiler - RCD tripped straight away

To discount the pump I unwired it - the RCD still tripped when turning the thermostat to fire up the boiler.

So I was thinking that this could be the room thermostat but then thought it's more likely to be the boiler. With just the hot water on the RCD didn't trip but this could be due to the hot water cylinder being full so the boiler wasn't heating any water.

What's puzzling me is why this only happens in wet and windy weather and only when the boiler fires up. The boiler is in the garage and has a vent pipe that goes out the side of the garage wall. What would be the next best cause of action? Get an electrician or plumber in or is there something else that I can do to further diagnose?

Thanks

Pete

[meow2222]

you already know how to divice and conquer, just carry on, divide more until youre only left with one thing that must be at fault. Then it will likely be easy enough to see why its tripping.

NT

[Roger Mills]

What actually switches the boiler on? Have you got any motorised valves? If so - certainly in CH-only mode - it will be a valve actuator which switches the boiler on after the programmer/room stat have told the valve to motor to the CH position.

So it could be a valve - rather than the boiler itself - which is causing the RCD to trip. I've no idea why this only happens in wet and windy conditions - unless the valve is located somewhere where rain water could be blown into its electrics.

[Pete]

Hello, Thanks for the replys - the RCD tripped again today (wet and windy weather again). With the central heating off, the RCD trips when the hot water comes on as well. The winds died down and the rains stopped and I can get CH and HW both on without tripping the RCD.

I had a look at the vent that comes out of the top of the boiler and I'm wondering if this could be the problem - the boiler vents out of the top, theres then a 90 degree bend and the the vent pipe goes through the garage wall and outside - this horizontal vent pipe to the outside is actually at an angle - it slopes down to the boiler - I would have tought that it should slope away from the boiler - could it be that the wind is blowing rainwater into the vent and then this is running into the boiler?

I'm unable to see any other valves that could get wet.

Thanks

Pete

Roger Mills wrote:

[John Rumm]

Is it a condensing boiler? If so then then flue should slope back toward the boiler, and it will be designed to accept water running into the flue. If however it is a conventional boiler then the flue should slope away from it a little.

Perhaps positioning a baffle a little in front of the flue to block the wind/rain would help diagnose if tis is the problem?