Boiler pressure problems...

[craigdeakin101]

Hi everyone,

I'm hoping someone can advise me on a problem I have with my bolier/CH system. It is a Worcester Bosch Combi Greenstar boiler.

Basically, the pressure (as indicated by the boiler) drops dramatically, but ONLY when the central heating is on. During the summer I have no problems at all. It has been like this since I moved in about 2 years ago, but has got gradually worse over time. Originally I was having to re-pressurise the bolier once a week, but now it has to be done daily, or even twice a day if I have the heating on all day. I am repressurising the bolier to approx 1.5 bar, and it is dropping right down to zero - normally when its at zero the radiators begin to crackle/gurgle which prompts me to repressurise.

All of the radiators are hot all over, so I dont think I need to bleed them.

The fact that I seem to be losing so much pressure makes me think I must have a leak somewhere in the pipework, but I cant see water anywhere, and if this was the case I would expect some leakage in the summer also?

As a bit of background information, I had British Gas out to look at the problem but they couldnt find anything wrong with the boiler itself. I also had Worcester Bosch out to replace the heat exchanger plate which was blocked up & causing the bolier to overheat when running the hot water, and I have had a power flush done by an independant company on the recommendation of Worcester Bosch. All of this was done about 1 year ago.

Does anyone have any suggestions/advice on what the problem could be?

Thanks for your help

Craig

 

[Breesey]

Check pressure of expansion vessel. You will have to do this with no pressure in the system.

 

[craigdeakin101]

Thanks for the response. Is there a how to or anything for doing that? I'm a bit of a novice with boliers...

 

[Breesey]

Specifically, which boiler do you have? You probably can't do this yourself as it requires case removal and it's inside the room sealed section.

 

[Whitespirit66]

Number 1 on the FAQS -

//www.diynot.com/forums/viewtopic.php?t=37170

You will probably find that the system's water is being lost through the copper pipe that runs from boiler, through wall, to the outside. Exp. vessel will either need repressurising or renewing.

 

[Breesey]

...but depending on which boiler you have you may not be able to do this yourself.

 

[craigdeakin101]

The boiler is a worcester bosch greenstar 35 CDI

 

[Breesey]

The boiler is a worcester bosch greenstar 35 CDI

I'm afraid I would hesitate to advise you to remove the casing of this boiler, which is necassary to check vessel pressure.

 

[craigdeakin101]

I decided to have a go at checking the vessel on Saturday (once the boiler pressure had dropped to 0 bar).

The vessel pressure was about 3 PSI, which I increased to 10 PSI. I then re-filled the boiler pressure to 1 bar through the filling loop and turned the central heating on.

Unfortunately, about 4 hours later the boiler pressure had dropped back down to zero.

Is there anything else boiler related that could be causing this?

Am I right in thinking that because it only happens when the heating is on, it cant be a leak in the pipework somewhere? Surely if there was a hole in the pipework it would leak all the time. If there is a leak it must be under the ground floor as there is nothing visible, and I am losing a lot of pressure!

thanks for your help

Craig.

 

[CBF]

the prv needs replacing

 

[craigdeakin101]

I thought I would post an update with the current situation...

I decided to attach a bag to the copper vent pipe on the outside wall to check if water was escaping (as I understand, if the PRV is faulty it will vent through this pipe). The bag was attached while the heating was on, and during this time the pressure dropped from 2 bar to zero (about 3 hours). The bag was bone dry, so the water must be going somewhere else?

I had a local gas engineer out yesterday, and explained to him what I had done so far. All he did was recharge the vessel (which I told him I had already done), and told me to contact Worcester Bosch if that didn't sort it. Needless to say that hasn't worked!!

I have read that if the heat exchanger is cracked, it can leak through the condensation pipe. I decided to unclip the pipe and put a bucket under it to see how much water came out of it. During the course of about 3 hours, 5 litres of water had collected in the bucket. Does anyone know if this is a normal amount of condensation from a combi over that period of time? It seems a lot to me?

I want to absolutely rule out the possibility that there is a problem with the boiler before I start taking up floors etc to check the pipe work.

Thanks
Craig

 

[craigdeakin101]

Just a final update to this thread...

The problem turned out to be a cracked heat exchanger which was leaking through the condensation trap (hence no visible signs of water). Worcester Bosch replaced the heat exchanger under their fixed price repair service £250, which is less than you can buy the part alone for, so well pleased with the result. The pressure is now holding firm, and the radiators get much hotter too which is an added bonus!!

Craig

 

[easyflow]

Job done