Potterton Puma 80e trips RCCB

[bernardgreen]

The Puma 80e in my daughters house will trip the RCCB in the consumer unit from time to time. It will run fault free for several weeks and then trip as soon as the power is turned on. ( because it trips all power in the house it is disconnected when the boiler is not required ).

No signs of leakage anywhere, no relationship to weather conditions.

No measureable leakage live to earth or neutral to earth when I was there ( but it was not in the tripping mood at the time )

Trips even when heating is off and no hot water demand.

I have provided an isolation transformer (with RCCB between transformer and boiler) to "protect" house RCCB and freezer contents. This trips from time to time. Once it has tripped it can be several hours before the boiler can be powered up.

First call by a local technician resulted in a new PCB being fitted, fault still re-occured.

I suspect either gas valve or fan have an intermittant short / low resistance path to chassis and hence earth.

Anyone had a similar problem ?

Boiler is located Preston.

Bernard Green
Sharnbrook
Bedfordshire

 

[simond]

I suggest you disconnect the pump and see what happens. They are in a position where water can get in the junction box in tthis application.

 

[nickso]

pumps and fans are the biggest culprit for blowing fuses although once they go they are generally off for good.

if it takes several hours to to get the power back after a trip that provides a good window for testing various components. if you dont get anything by your fluke meter sometimes the only way to go is by disconnecting bits one by one until you find the bugger. remember to check the mains wiring to the boiler from the consumer unit as well.

probably not an easy one to find this one

 

[bernardgreen]

pumps and fans are the biggest culprit for blowing fuses although once they go they are generally off for good.

if it takes several hours to to get the power back after a trip that provides a good window for testing various components. if you dont get anything by your fluke meter sometimes the only way to go is by disconnecting bits one by one until you find the b*****r. remember to check the mains wiring to the boiler from the consumer unit as well.

probably not an easy one to find this one

Certainly not easy. It is a 150 mile journey to get to it and if I set out the b*****r will clear itself by the time I arrive.

The use of the isolation transformer right next to the boiler confirmed the fault is definately in the boiler or thermostat wiring.

To save my daughter un-necessary expense I need to prove which item is faulty before changing it.

 

[nickso]

it will be difficult to do it the way you want to as the boiler probably isnt going to do you any favours by the sounds of it.

the way i described above is the easiest if not the most convienient

dont discount any wiring up to the boiler side of the rcd you have installed....many a headscratching hour lies that way

 

[bernardgreen]

it will be difficult to do it the way you want to as the boiler probably isnt going to do you any favours by the sounds of it.

the way i described above is the easiest if not the most convienient

dont discount any wiring up to the boiler side of the rcd you have installed....many a headscratching hour lies that way

Aware of that. Been there

The isolation transformer means the RCCB installed between transformer and boiler only reacts to faults in the boiler.

 

[Agile]

In view of the distance my advice is to change the pump anyway as thats the most likely cause.

You need to test at mains or 500v as most of those faults do not show up with an LV test.

Tony

 

[bernardgreen]

Thanks for the advice.

Problem appears to have been solved by fitting a new pump. The old pump has clear signs of damp having reached the terminals.

It was confusing as the pump does not normally run if there is no central heating demand so why would it trip immediately the boiler's isolator was turned when the CH switch was in the OFF position.

Answer is that when power is applied to the boiler the pump does have power applied to it for a very short duration. As the PCB "logic" sorts it's self out from the random state at power up the relay controlling the pump energises for a random length of time ( less than a second ) which results in the damp pump tripping the RCCB.

Discovered that many other houses on the development are having similar problems with the Puma 80. Apparently they are too large for the size of house among other things. Tripping RCCBs happens in a couple of houses.

Bernard Green
Sharnbrook
UK

 

[Agile]

There is no "logic" circuitry on the Puma in the normally accepted digital sense.

The Puma is certainly not over sized for any property. Its a 24 kW boiler which is the minimum power ever used for a combi.

The current trend is to fit a minimum of 28 kW for a combi.

Tony Glazier

 

[bernardgreen]

There is no "logic" circuitry on the Puma in the normally accepted digital sense.
Tony Glazier

I used the inverted commas around the word "logic" for that reason.


Regards

Bernard