RCD issue with boiler

[fez]

Hopefully someone on here can help me before I spend a lot of money on an electrician.

Have edited because I have found the location of the fault. When I disconnect the central heating pump the whole things works fine (apart from no hot water being sent around the house obviously).

Is this likely to be a case of buy and fit a new pump or could the issue be elsewhere.

 

[toyotacelicagt4]

Check for loose wiring going to the pump. If all looks ok then the pump will need replacing

 

[fez]

Check for loose wiring going to the pump. If all looks ok then the pump will need replacing

I had kind of resigned myself to replacing the pump. I did a resistance test across the L/N terminals on the pump and it read about 202ohms which another website suggested meant that the pump was fine. Honestly, the pump is old and a replacement is about £100 and I have spent a good while on this already so I might just replace it and see if that fixes the issue.

 

[bremen1874]

What else is on the same circuit?

It's the combined earth leakage on the circuit (or rather the circuits connected to that RCD) that matters so it isn't necessarily a single device causing the tripping.

RCDs can become over sensitive as they age.

I fixed the nuisance tripping that seemed to be caused by my drier my moving the garage circuit to the other side of my consumer unit. Both sides have the same type of RCD, but it no longer trips.

 

[FlyingFish]

It's quite common for pumps to do this when they are close to failure or the motor gasket leaks allowing moisture in. Just swap the pump and move on

 

[Adam_151]

I did a resistance test across the L/N terminals on the pump and it read about 202ohms which another website suggested meant that the pump was fine.

Unfortunatly the other website was not exactly wrong, but certainly not giving the full picture. While that reading does suggest good continuity of windings, thats not really what we are intereested in here what matters with regards to tripping RCDs is the insulation resistance to earth, now to measue this properly you need an insulation tester and you'd want to see at least 1Mohm ( 1000 000 ohms) between the winding and earth (disconnect pump L&N from circuit) Now you can have a look at it with a mulimeter and if you get something to earth then that would indicate a problem, however if you don't then that doesn't indicate a lack of a problem (because the issue might not be showing up at the much lower test voltage) so its a test for badness, not a test for goodness...

 

[fez]

Just a quick update, I pulled all the wires out of the pump and suddenly water was coming out of the pump. Took the plate off that secured the electronics facing to the pump and the inside was full of water. Coils and electrics were sodden. Think that probably answers the question of whether the pump was the issue and needs replacing.

 

[fezster]

If you buy a replacement pump and want to fit yourself - be aware that the old pump valves will probably need replacing too, which means draining down the system may be necessary.

 

[fez]

Cheers for all the help guys. What do you mean the pump valves fezster? As in the ones above and below the actual pump unit that allow you to cut off flow to the pump completely (in theory). I have heard a few people suggest that there might be a problem getting them to completely stop the flow but it sounded more like a small leaking from the valve rather than something that would get in the way of replacing the pump.

Since the pump went, another little bit started leaking as well which I am planning to leave until I replace the pump and see if that sorts itself out. The bottle air vent is leaking very very slowly. Is that likely to be because the pump isn't working or is that simply coincidence that the pump and air release valve have gone at the same time.

 

[fez]

New pump arrived and obviously when i close the valves either side of the pump there is still a fair amount of water coming out. I'm assuming that one or both of the valves are buggered. What should I replace them with as reviews for the replacement parts seem to suggest that these failing to close off properly is par for the course. From what I can see, I am going to have to drain the whole hot water system down to do this.