Intermittent central heating fault..

[Bluetit]

Hi,

I've recently looked at a fault with an intermittently tripping RCD at a property for a landlord I do the odd job for.
Got there and did the basics, IR'd the cables, looked at resistances across the pump, got acceptable results everywhere I looked. Played with the heating, demanded hot water and central heating to try and recreate the fault. Absolutely nothing. Apparently it is very sporadic and can be days apart, which given the time of year means the heating does not trigger it every time..

The CU wasn't split sensibly to my mind with up and downstairs lighting and smokes on one RCD and heating, ring and oven on the other, I swapped the heating with one of the lighting circuits, to see if the fault moved, to give a slightly better split, and to be sure it wasn't due to some sort of cumulative high leakage from things plugged into the ring.

The fault has indeed followed the heating across to the other side of the CU. I am happy to admit I'm competent with domestic heating, but it's not my bread and butter, and am now scratching my head, mostly due to acceptable test results and the lack of repeatability.

It's a small 2 bed property with a Y plan set up.

Any thoughts would be much appreciated.

Thanks.

 

[Pretty Mouth]

IR'd the cables

just the cables, or did you keep equipment in circuit?

 

[Bluetit]

just the cables, or did you keep equipment in circuit?

I removed the equipment, then tested the equipment separately where I could eg. Looked for a resistance that looked sensible for a pump or valve actuator.

 

[Pretty Mouth]

I removed the equipment, then tested the equipment separately where I could eg. Looked for a resistance that looked sensible for a pump or valve actuator.

Did you IR the equipment? L+N to E at 250V?

 

[SparkySy]

Did you test the mid position valve whilst moving the lever, I have had them fail IR testing in a certain position before, so weren't easy to diagnose.

 

[Bluetit]

Did you test the mid position valve whilst moving the lever, I have had them fail IR testing in a certain position before, so weren't easy to diagnose

Did you IR the equipment? L+N to E at 250V?

I did not, I did at from the CU, but as mentioned above I need to go and IR the kit while manually shifting the valve about.

I'll go and do this when I return to swap out the meter box hinges that have failed and report back. Seems like an incredibly obvious thing to check now

 

[Bluetit]

Update.
Went back today as it was popping the other RCD post move, again intermittently with no real pattern. Typically overnight but not every day.

IR'd the valve throughout the range and everything was fine, pump fine, stat. wiring all fine too. Upon pulling the god awful rats nest all the way out of the wall behind the controller (no box, nothing just connector blocks and shoved into the stud...) the room stat has a pre-heater in it which the neutral at the control end was either never connected, or not put into in the connector block properly, but eventually pulled this out of the wall hanging around bare copper ended. There was no obvious short to earth when testing this, but this is the only thing I can find as a cause. Now put away safely (or as safely as it can be under the circumstances!). Back to waiting, if it still pops I'm now at a loss.