Methodical fault finding for boiler

[Brigadier]

Hello all,

I need help with a method to eliminate potential problems with my boiler, so that I can get the real problem sorted (by a pro!)

The problem is that the pressure continues to creep up, at the rate of about 0.3bar per day. Boiler is a potterton performa 28.

Quick brain dump of facts....

I can turn off the main stop tap in the kitchen.
I can't turn off the cold water tap directly below the boiler (seized).
Filling loop is still connected (although the tap is shut). How "off" it actually is, is not known to me.
Pressure goes up and down when using heating and / or hot water, and always ends up slightly higher in the end.
Heating is currently on timed (kids and missus at home), and how water used as and when, so I probably can't currently switch everything off, to see what happens.
I drain off a couple of litres every few days (via the downstairs draincock), to keep the pressure at around 1.5 bar cold.



My initial thoughts are:

filling loop could be passing (but as I can't budge the tap below the boiler, I'm afraid to disconnect it in case of flood!)

expansion vessel not working properly.

dhw heat exchanger pinholed.

ch heat exchanger pinholed.



Are there any tests that I can safely do for each (given the stoptaps that I can't shut off, etc), to enable me to rule out some or others of the possible faults? Are there any other faults that may be occurring?


Thanks in advance

 

[Agile]

You seem to know all the things which you cou do but are frightened of causing a flood or disturbing your family.

In that case I would say that you have reached the limit of your capabilities and its time to call a professional heating engineer.

You have previously mentioned having a friend who is a heating engineer. I dont understand your reluctance to call him, another independent or British Gas.

Tony

 

[oldbuffer]

For the pressure to build up, fresh water must be entering the heating circuit at some point. This could be either:
a. The filling loop if the valve(s) aren't closing properly.
b. The plate heat exchanger for the domestic hot water (DHW) which might be leaking.

If you are able to turn off the mains stop cock in your kitchen, see if the hot water stops at the same time. If it does, it suggests there is no flow going to the boiler DHW cold water feed.

As the filling loop is normally taken off that feed, you could then try slightly loosening the "post valves" side of the loop (the one that connects to the central heating return pipe), with the valves turned off. Then gently turn the kitchen stop cock on again.

If water starts to come from the loosened connection, then both valves that should shut off the filling loop are allowing water through. If they are not, then it is probably time to call someone to check the heat exchanger. If you are brave, you could forget the stop cock bit and just slacken the filling loop connection.

 

[paulwrx]

Its the filling loop...the end...dont forget to thank me

 

[JPC]

you say that paul...however it took me some time to sort out a problem of over pressurising on a combi the other week.

symptoms were that the boiler was always at around 3 bar....open prv...drops but them comes back up..initial thought dhw heat exchanger had gone...ordered one.

on returning to the job a day later, thought id look at it again before swapping it...closed the cold water to the boiler...still 3 bar. u could run some water off and it would drop in pressure but it would then come back up within around 5 seconds, to 3 bar.....

did loads of things...incl filling loop (first thing i did)..i concluded there had to be water coming into the central heating system somewhere...

after looking for 45 mins i found a cold water mains, plumbed into the return pipe via an open stop tap, under the very back of the cooker ...

so pressume nothing !!!!

 

[45yearsagasman]

Its the filling loop...the end...dont forget to thank me

Some quality fault finding there.

 

[Brigadier]

Thanks for the prompt replies all

Agile - thanks for your considered post. My only thing with calling out my friend is that I was wondering whether there were some "tests" that may need to be run for a few days, and therfore I could do them when convenient, rather than him having to come out, shut something off, leave us all freezing for a week, then come back to check the results. Convenience and time-saving, that was my thought

 

[Brigadier]

after looking for 45 mins i found a cold water mains, plumbed into the return pipe via an open stop tap, under the very back of the cooker ...

Jeez - was there any logic in that?

 

[Agile]

I would say that the first thing that should be done is to replace the seized valve!

Tony

 

[mickyg]

get the water off in the street, change your stop cock, drop the CH pressure and change the complete filling loop to a proper one with 2 isolators. If your really unlucky you've got a holed plate he, but Its quite rare and i've never had it on a performa before. Worcester CDis are usually worst for it.

 

[Boilerman2]

At least a Plate HE for a Performa is cheap as chips

 

[mickyg]

At least a Plate HE for a Performa is cheap as chips

unlike the bloody washers it seals with. £2.60+vat each i got robbed in PC today, ridiculous. How do you convinve a customer that small rubber washers cost £3 each ffs.

 

[petit_pablo]

unlike the bloody washers it seals with. £2.60+vat each i got robbed in PC today, ridiculous. How do you convinve a customer that small rubber washers cost £3 each ffs.

If they moan, fit the plate heat ex without the washers! See what they think they are worth after that

 

[Agile]

unlike the bloody washers it seals with. £2.60+vat each i got robbed in PC today, ridiculous. How do you convinve a customer that small rubber washers cost £3 each ffs.

Thats easy!

Just tell the customer that British Gas charge £6 each for the washers!

Think of that BG door leaflet that says an independent charges £300 to change a pump and £210 for an APS.

If thats not enough point out that the key for a Merc is £300 because you cannot start the car without the key!

 

[twgas]

Just tell the customer that British Gas charge £6 each for the washers!

cheepskate, we need the job to go over £200 to get bonus!