Potterton Combi 80 nightmare

[S&LBaillie]

Hi all,

im hoping somebody can help us with our boiler nightmare!

We've got a Potterton Combi 80 boiler which is losing pressure like nobody's business!.

After reading all the previous posts about pressure lost we are now at a loss as to what to do next.

For the past few weeks my husband has been refilling the boiler about 2/3 times a day to 1.5 bar and within a few hours it is back to 0.

There are no leaks on the radiators and we have ripped all the carpets up to check the pipework under the floor.

The PRV is not dripping as we have had a bag over the end of the pipe and no water lost.

This morning i turned the heating switch off so i could run the water without blowing up the damn boiler and managed 1 bowl before it started to make clicking and hissing noises. The i noticed the AAV had blown its fuse and steam was coming out the top.

My hubby replaced the cap on the top of the boiler and re-filled (AGAIN!) to 1.5 bar so we can heat the house.

When the heating is on it stays around 2 bar and as i remember from prev posts this is ok as long as it doesn't keep rising as then it could be the expansion vessel?.

Any ideas folks? Any help will be gratefully received!

Louise

 

[corgiman]

sounds like the pump is not working

without the pump running the water in the boiler will, well, boil! hence the steam coming out of AAV. It will also expand the water loads, more than the expansion vessel can handle.

Also the wax diverter valve in these combis are rubbish and fail, thus not allowing the water from the boiler to flow to the rads and this will also cause the above.

so you will need a corgi person to change which of these is the problem.

 

[S&LBaillie]

Hi, thanks for the quick reply.

The pump seems to be working fine and i think the only reason the AAV blew was because the pressure was just on 0 this morn (being impatient i couldn't wait for hubby to refill before using water!).

When we re-fill the system to 1.5 all the rads work fine and get hot, even the ones upstairs.

Help!

 

[corgiman]

do any of the pipe run under concrete floors? if so and they wernt protected adequately then they have probably corroded

 

[S&LBaillie]

Hi,

All the downstairs of the house has concrete floors.

We've checked all the floors as we did have a pipe burst under the lounge floor about 3 yrs ago and it was replaced.

2 yrs ago we had the whole system checked as we had a problem with the water pressure in the bathroom taps. The system was completely drained and new inhibitor put in. since then it has run fine.

We had a corgi man around last week who advised us to check under all the floors as he couldn't find anything wrong with boiler.

When the PRV leaks how much do we need to see (ie-drip or big leak) for this to be the cause?

Any ideas?

 

[corgiman]

well to de pressurize it totally it would be a fair amount, and its emptying itself twice a day, I would say you have a fair old leak somewhere, and the favourite place for it would be under the concrete soemwhere, if it were upstairs you would have noticed by now.

 

[S&LBaillie]

Our thoughts exactly but we cant find one!

Our lounge is 30ft long and we have had all the carpet up. The pipes don't run very deep under the concrete so when we have had a leak before it was easy to find as the carpet was wet.

Im getting worried as surely we'd be swimming by now as it's been happening for a few weeks!

Upstairs has wooden floors and as you said we'd definitely have noticed by now as it would be coming through the ceiling!

 

[corgiman]

yyou would not nessessarily notice the leak under concrete as it is porous, still think thats where it is

 

[S&LBaillie]

Is there any way a Corgi plumber can trace the leak using todays modern technology?

Could it be anything else?

Lots of posts mention the expansion vessel as a problem, although i think thats if the pressure is going up not down!

 

[corgiman]

nope not that I know of

Does anyone else?

as for the expansion vessel, is the pressure hitting 3 on your guage at any time? if not the it aint the expansion vessel, also the pressure relief valve you say is not leaking, if the expansion vessel ahd goen it would be

sorry

 

[S&LBaillie]

Ok thanks for all your advice.

Pressure doesn't ever reach 3 so not the EV.

Will keep an eye on the PRV pipe and the floors for leaks.

thanks again

 

[ChrisR]

If the heating's on max (CH water would be at 82º C or so) and there's leak in the floor the floor will heat up around the leak - if it doesn't all go straight down.
Then you can use Infra red thermometer to look for it They are quite reasonable now (£20 up). Or Thermal Imaging - which , unless you have a mate in the fire brigade, could be pricey.
Only other solution is to dig, cut pipes, test parts of the system with a pressure tester... You're going to have to dig sooner or later. You may need a CAT to find where the pipes go if you can't follow the heat.

 

[corgiman]

what a craking idea chrisR

Never thought of that

cheers

:

 

[Agile]

Another possibility is to isolate the downstairs heating circuit and run the boiler with the upstairs heating and see if it still looses pressure.

If so as we expect then you have a leak in the concrete. One possibility if that is the case is to pressurise the pipework to three Bar which will exercerbate the leak and it may become visible.

Tony Glazier

 

[bones001]

Have you had a look in the combustion chamber on the boilr, the heat exchanger could have a crack in it and leaking from there.