Potterton Combi 100 tripping RCD

[DaftGeordie]

Hi,
I've got a problem with my Potterton Combi 100 in that it is tripping the RCD on the electrics breaker box.

The background is that in the last couple of weeks the RCD has been tripping on an irregular basis, sometimes once a day, sometimes 5 times in 10 minutes.

To isolate the culprit I powered off and unplugged EVERYTHING and plugged back in one appliance at a time. As the problem is intermittant, I went through this exercise a number of times until I am as certain as I can be it's the boiler.

Now the RCD will trip with ONLY the boiler powered up, but it's not always "doing" anything (ie heating is off - it's the summer!) and no taps on. It trips more regularly when the HW tap is open full.

I had a CORGI guy come around this evening and after a *very* quick look (3 mins, £70, thanks very much) he reckons the pump is fine, the PCB is fine and that the issue is the wiring loom. And to add insult to injury, he reckons the only "fix" is to replace the ENTIRE boiler!

So, two questions:
1. Is his diagnosis of the wiring loom being the likely culprit an accurate one?
2. Is there a resolution which doesn't require a full boiler replacement (suuuuurely )

Thanks in advance,
DjP
PS We are selling the house, so while we don't want the new owners to have a crippled boiler, I don't want to over invest either!

 

[gas4you]

Are there any signs of water leakage onto any eletrical componets, switches etc?

If it is the RCD tripping then there is a leakage to earth somewhere, either live or neutral.

The usual most common culprits are the fan or the pump. How he could diagnose whether anything is working or not in 3 minutes is beyond me

It could end up being the loom, but more often than not it's the bits on the ends.

 

[Gasguru]

It's customers such as you that really **** me off. If you had more bo**ocks and didn't pay these cowboys the industry wouldn't have the reputation it deserves.

Even allowing for travel £70 to tell you nothing is rip-off.

Turn off the power and pop off the front outer cover, drop down the circuit board box. Have a look at the circular brass lump (hot water flow switch). Check water is not leaking from the switch end (with the hot tap on full)....it drips onto the connector block below. Also check the connector block for cooked wiring (terminal screws may be loose).

Next have a look at the auto air vent (top left). Water can leak out down the left side of the combustion chamber and into the gas valve connections.

Next have a look at the flow thermister sensor (just above the pump)....these often leak and sometimes over the pump connections.

These are the most common leaks.

If you are competent disconnect the pump wiring and wire the pump directly to the mains via a 3 amp fuse. With the boiler off run the pump and see if the RCD trips.

 

[DaftGeordie]

Thanks for the prompt reply guys - as predicted, there's water very slowly dripping from the "circular brass lump" onto the "chocolate box" connectors and wires below. Electricity and water? Hmmm...

Is there a fix for this or do I need a new brass lump? (Sorry if I'm getting technical).

Finally, know anyone REPUTABLE in Guildford area who could sort this for me?

Thanks again for the help, I've been going mad with this...
DjP

 

[Gasguru]

Yes replace the brass flowswitch assembly. You may also want to change the actual switch since these can become waterlogged and fail. Parts around £30.00 and a couple of 1/4 washers. There's plenty on the forum (search) to change it yourself otherwise a 1/2 hour job plus the safety checks (and drying out the connectors).

As for the rgi...phone him up and tell him what a to**er he is, ask for your money back or mailshot his neighbours.

 

[DaftGeordie]

Thanks again for the info - all makes sense when you hear from someone who knows what they're talking about.

Needless to say, I've cancelled the cheque...

 

[spacethegas]

gasguru

i might get to like you

 

[Vic Spanner]

It's customers such as you that really p**s me off. If you had more bo**ocks and didn't pay these cowboys the industry wouldn't have the reputation it deserves.

Sums it up nicely...Well said