Potterton Suprima 80 CH trips electrics, HW ok

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Hi everyone, I need some help before I spend any more money. I am not a plumber but will give the information as accurately as I can. My boiler (old Potterton Suprima 80) is tripping the whole house rcd when the central heating is put on. It runs for a few seconds, 10 minutes or even a few hours, but then it trips out. This does not coincide with the pump or the fan or thermostat clicking on. The hot water is working fine and will run alone with no problems.
We have had a new zone valve put on, no difference. We have had a new thermostat, no difference. We have unplugged every appliance on the circuit and just run the central heating, no difference.
Plumber says maybe pump, maybe fan, maybe pcb, but I've already spent £700 and still have no heating. I am at my wits end and rowing with my poor husband about it. I just don't know where to turn next and don't want to spend any more money on anything that isn't going to fix the problem.
Can anyone offer any guidance? I'm looking at a cold cold Christmas! Thank you! Lucy :)
 
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The fault is very unlikely to be in the boiler.
Is your hot water feed pumped or gravity (suspect it is pumped cos you mention a zone valve but no harm checking).
Are the zone valves 2 port or one 3 port?
If hot water primary is pumped then the fault is likely to be in the wiring to the heating thermostat or controller.
You probably need an electrician with some proper test gear (not a multimeter) rather than a plumber- isolate the boiler, check the cabling. All of it- N-E faults can be tricky to localise.
If you have 2 port valves and pumped hot water you can use the manual override on the heating zone valve to get some warm to the rads while hot water demand is present. You can manually override 3 port valves but you'd have to disconnect some cables....
 

CBW

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Agree with above, unlikely to be the boiler. Has the plumber tested any components or just guessed and replaced?
 
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How can you have spent £700 on just a zone valve & thermostat replacement, whatever the make the parts are well under £100.

Find an electrician with a earth leakage clamp...it should be straightforward to find the problems.
He can also test the RCD is within spec (they can "wear" out leading to false tripping).

https://www.test-meter.co.uk/electrical/clamp-meters/earth-leakage-clamps
 
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Hi, Thanks for your help so far.
I need to check some of the points the first gentleman gave me, but will report back once I know.
Re parts replacement question - guessed and replaced, that's why I'm so upset - I feel this could go on and on with me getting poorer and poorer and colder and colder :(
Re comment about how much I've been charged. Feel even worse now :(
 
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Post a pic of your invoice...scrub out his name.
9/10 it's water in the pump but you say it's fine with the hot water so that would normally rule that out.

RCDs detect the total fault current and there's always a chance the boiler trips it but the fault lies elsewhere....hence an electrician with the test gear is often better at locating the problem.
 
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****e boilers. Probs the PCB.
Maybe not.

Did you change anything before this started happening?
 
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Hi oldbutnotdead - I have answers for your questions -
Hot water feed is pumped. The zone valve is 2 port.
I do get a little warmth through the radiators when the hot water is firing. (Much money wasted trying to sort that out in the early days of owning the property, something to do with some rogue piping somewhere when various extensions were put on. In the end I gave up and just turn the offending radiators off by hand in the summer.)
The buttons on the central heating controller box are a bit 'sticky' (don't go on and off cleanly) so maybe it is that...
Thank you so much for your help. Logically it seems to me that it has to be an electrical fault, so I will pursue that and not give more money to the plumber on a guessing basis.
Any other suggestions/help gratefully received.
I will post if (hopefully when) I get it sorted out so that others can benefit.
Lucy :)
 
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CBW

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Which 2 port was replaced? I’m guessing the heating? When you run just the heating, does this still trip electrics?
 
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Hi Chris,
Yes and yes. I tried running just heating without water this morning and it tripped. I also tried unplugging everything on circuit and running heating and it tripped.
I am so glad I've found you all! I thought I was going mad yesterday. :)
 
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Hi oldbutnotdead - I have answers for your questions -
Hot water feed is pumped. The zone valve is 2 port.
I do get a little warmth through the radiators when the hot water is firing. (Much money wasted trying to sort that out in the early days of owning the property, something to do with some rogue piping somewhere when various extensions were put on. In the end I gave up and just turn the offending radiators off by hand in the summer.)
The buttons on the central heating controller box are a bit 'sticky' (don't go on and off cleanly) so maybe it is that...
Thank you so much for your help. Logically it seems to me that it has to be an electrical fault, so I will pursue that and not give more money to the plumber on a guessing basis.
Any other suggestions/help gratefully received.
I will post if (hopefully when) I get it sorted out so that others can benefit.
Lucy :)

May i suggest (You won't like this but....)

That boiler is old, likely clapped out and has been surpassed by modern tech, as has the controller, the zone systems and rad valvs and the stats etc, etc.
Whatever you do with the boiler, you will be replacing it in the next 5 years anyway i imagine. I am looking at my Suprima which has had its guts replaced over the years and i'm not looking to fix it anymore. Its 20 years old. time for it to move on...

At the risk of repeating myself (Harry), Look to putting in a new system.
New boiler, controls, tank, etc, etc.

Gas prices are going to rocket, so getting a efficient, well run system will pay dividends in time.
Fit smart controls to the system and stop being tied down by old tech limitations, ditched the zone approach.

If its Boiler (PCB) they are expensive to replace if you don't do it yourself and you will likely find yourself looking at a new boiler solution anyway
If it's not boiler, suggest that you don't buy something expensive to replace something whatever it is that isn't working. Just buy a basic doohdah to get you going and look to upgrade the whole thing as soon as you can.

Something to think about.
And delete that plumber from your contact list :)
 
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If you set programmer to domestic hot water only ,and manually latch open the central heating zone valve ,does RCD still trip ? You would need to do the above ,when hot water cylinder is cold ( in other words needs domestic hot water to be heated ,or boiler won't fire up )
 
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Hi blueloo, I know in my heart, it's inevitable, but I've just had to replace my 19 year old Volvo, which finally stopped being worth repairing and I just can't do another investment at the moment, although I know it's coming and soon! I've got to find a way of limping on with this system for a year or so if it's possible.
 
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If it comes to it a MCOL should get much of that back...no "plumber" wants a CCJ on their record.
There's no mystery to leakage currents just gross incompetence in the trade....if you've haven't got the test equipment or knowledge to investigate you've no business attending.
 
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