Rcd tripping issue.

[Pauldicker]

Can someone shed some light on a problem I'm having.
I changed a CU today as there were only 6 circuits they are all now rcbo's there was no rcd protection prior to that.
On the ground floor circuit the rcd test was x1@ 147ms and x5@ 23ms.
However now when the customer turns the heating on its fine and if they turn the hot water on at the same time it's tripping the rcd.
It is run from a fused connection unit and upon looking all looks good in the fcu.
It's a valiant ecotecplus 618 and the controller is a lifestyle lp522
I'm not a heating engineer but I may be missing something obvious.

 

[Pete999]

Can someone shed some light on a problem I'm having.
I changed a CU today as there were only 6 circuits they are all now rcbo's there was no rcd protection prior to that.
On the ground floor circuit the rcd test was x1@ 147ms and x5@ 23ms.
However now when the customer turns the heating on its fine and if they turn the hot water on at the same time it's tripping the rcd.
It is run from a fused connection unit and upon looking all looks good in the fcu.
It's a valiant ecotecplus 618 and the controller is a lifestyle lp522
I'm not a heating engineer but I may be missing something obvious.

Any test results prior to swapping the CU

 

[The Ghost]

Spose I would start on test the circuit in question with IR test see what comes up but then as Pete says, you would have already done that ?

 

[Pauldicker]

Any test results prior to swapping the CU

No other than it was working before.

 

[Pauldicker]

Spose I would start on test the circuit in question with IR test see what comes up but then as Pete says, you would have already done that ?

Would that be with the boiler connected and disconnected. The ir results were within limits but its older cable so allowed for the drop.

 

[Octopus]

I think you have sort of answered your own question here.

1. I'm assuming you did the IR tests on the circuit from the CU to the boiler FCU

2. The heating is switched on and works

3. When the boiler "calls" for water, the RCBO trips.....

 

[The Ghost]

Logically if it trips when the hot water is turned on its in the boiler. I do know they have a motorised screw valve that is prone to leakage they may have this valve leaking. It operates when you call for hot water. When did they have their boiler service last. Its such a small leak that you may not see it outside the boiler.

 

[Pauldicker]

I think you have sort of answered your own question here.

1. I'm assuming you did the IR tests on the circuit from the CU to the boiler FCU

2. The heating is switched on and works

3. When the boiler "calls" for water, the RCBO trips.....

Well i did not dosconnect the boiler or switch the fcu off so tested it all.

Yes the heating works but if you call for water at the same time it trips. However what seems strange is the heating works now when you call for water on and the heating button does the tripping. Im wondering of the controller is knackered.

 

[Midwest]

Have you tried easing the controller and associated wiring behind it, to see if the fault replcates itself? Is there a room stat, cylinder stat & associate wiring?

 

[Pauldicker]

Logically if it trips when the hot water is turned on its in the boiler. I do know they have a motorised screw valve that is prone to leakage they may have this valve leaking. It operates when you call for hot water. When did they have their boiler service last. Its such a small leak that you may not see it outside the boiler.

Yesterday they had serviced and we rang him. His answer was "it was working yesterday" obviously as there was no rcd prior to today then it would have worked and the CB would not trip.

 

[Pauldicker]

Have you tried easing the controller and associated wiring behind it, to see if the fault replcates itself? Is there a room stat, cylinder stat & associate wiring?

Yes all of that. I did remove the controller but did not prod around inside.
When you turn the room stat off the boiler did not shut down we had to turn the controller off.

 

[Midwest]

I would consider swapping RCBO's, IR boiler and associate wiring (speaking to valiant technical first).

 

[Midwest]

When you turn the room stat off the boiler did not shut down we had to turn the controller off.

Well that warrants further investigation. You'll have to start at the beginning and go through it logically. Call valiant technical, this may a common fault.

 

[Octopus]

Well i did not disconnect the boiler or switch the fcu off so tested it all.

So if you didn't disconnect the "load" and you stuck 500v into the boiler, you may have damaged the boiler circuitry.

Tip: ALWAYS disconnect loads before doing IR tests AND not you think you have a fault, you MUST disconnect the boiler from the FCU and test the circuit PROPERLY so that you can eliminate this from your investigation.

What exactly were your IR tests? and how/where did you do your Zs tests?

 

[Pauldicker]

So if you didn't disconnect the "load" and you stuck 500v into the boiler, you may have damaged the boiler circuitry.

Tip: ALWAYS disconnect loads before doing IR tests AND not you think you have a fault, you MUST disconnect the boiler from the FCU and test the circuit PROPERLY so that you can eliminate this from your investigation.

What exactly were your IR tests? and how/where did you do your Zs tests?

Zs at db was 0.35 ir was done at 250v however i took out the earth and neutral fly lead from the earth and neutral bar. And tested then i may have been doing it wrong. Its a wylex rcbo.