Baxi Combi Instant 80 HE - Pressure problems.

[Arrowmaker]

Hi,

This is my first query having tried a local plumber who failed to turn up or let me know he wasn't able to see me despite me spending all day waiting for him and ringing him to check if he would still be coming 3 times. Gripe over.

My boiler works OK when the weather is not too cold with the operating pressure between 1 and 2.5 bar. Early last year with the snow on the ground it stopped and my daughter's boyfriend who is himself a plumber (they have now split up more the pity) re-pressurized the system as the pressure gauge was reading zero. This seemed to do the trick and it worked all throughout the year and including the freezing cold weather over last November, December and January. However this week after a few nights with the temperature dropping below freezing again I woke up in the early hours of the morning to find the boiler had turned itself off. There was no pressure reading on the gauge plus the pump/low pressure red warning light together with the lower green tap light were flashing. I turned on all the radiators and re-pressurized the system as shown previously. The boiler started up automatically and continued to work normally however over about an hour the pressure gradually dropped and the boiler cut out again with the two flashing lights back on.

In order to keep the pressure up I left the inlet taps on slightly watching to make sure the system pressure stayed below 3 bar then went back to sleep. That same morning I phoned the aforementioned plumber and turned off the inlet tap.

Having had no response from the plumber that evening I checked the pressure, which was holding steady, so decided to leave well alone. Last night and today the boiler has been working perfectly operating within the normal operating range 1 - 2.5 bar.

The overflow pipe does not run to a bent copper pipe on the wall, instead it is plumbed into the toilet drain/vent pipe, at least I think that is what it is so I can't tell if there has been any leaks to the outside from the boiler.

All the radiators work normally, no cold spots and all bled with no air in them. There appears to be no leaks anywhere around the house, inside or out.

I am of the opinion now that when we have sub zero temperatures for some reason something causes the pressure to drop and the boiler cuts off - but if so what?

Any help or advice would be most appreciated.

Thanks.

 

[bengasman]

Simple answer: pressure loss = leak.
Termination of prv must be visible, so that is done wrong.

 

[Arrowmaker]

If as you say the simple answer is a leak then why did the boiler work for the best part of a year before deciding to drop its pressure all of a sudden to below 0.5 bar in the early hours of Saturday morning causing it to turn off?

What was causing it to drop from 3 bar to 0.5 bar over the period of an hour early Saturday morning yet from Saturday mid day stop loosing pressure altogether and since then has been behaving normally operating within the 1 to 2.5 bar range also bearing in mind that the night time temperatures these past two nights have been around -2 to -3 degrees the same as Saturday morning?

Sunday night I switched the timer to go off during the day whilst I was at work with daytime temperatures around 10 degrees and then switch back on in the early evening which it did without problems and is now at this moment in time apparently operating normally.

With regard to the PRV outlet showing I must admit it would be convenient to see what is or is not happening but it was like it when I bought the house about two and a half years ago. I am not aware of it being mentioned in the buyer’s report.

Does anyone have any other ideas what might be wrong or if it is a leak where is it coming from and what is causing it. All radiators are operating normally with no cold spots or noises and have been bled twice without problems, there being no air in any of them?

Many thanks.

Pete.

 

[alwest197]

I have a Baxi 105e and had similar problems to yourself albeit after numourus other issues. I found that the pressure relief valve was stuck slightly open so that it would on occaision leak. It was fixed by replacing the internal bits of the valve. It was done by the original installer of the system and took him about 5 mins plus 30 mins testing and checking.

this could possibly be the issue, on mine I could see the water coming out of the pipe as you can't see yours its probably worth a punt..

I bought a new PRV off eBay but he only used the internal bits...I think it was about £12.

 

[bengasman]

If as you say the simple answer is a leak then why did the boiler work for the best part of a year before deciding to drop its pressure all of a sudden to below 0.5 bar in the early hours of Saturday morning causing it to turn off?

My first guess would be a combination of poor install and inadequate maintenance.

What was causing it to drop from 3 bar to 0.5 bar over the period of an hour early Saturday morning yet from Saturday mid day stop loosing pressure altogether and since then has been behaving normally operating within the 1 to 2.5 bar range also bearing in mind that the night time temperatures these past two nights have been around -2 to -3 degrees the same as Saturday morning?

Sorry, my crystal ball isn't working and without that I can't say without being there.

With regard to the PRV outlet showing I must admit it would be convenient to see what is or is not happening but it was like it when I bought the house about two and a half years ago. I am not aware of it being mentioned in the buyer’s report.

Not being in that report does not alter the fact that it is a legal requirement.

A buyer's report will hardly ever find this kind of problem as it does not involve a full survey of a RGI. For the same reason, your house will probably have many electrical inconsistencies because there was no inspection by a qualified electrical inspector.

 

[Arrowmaker]

Can I first of all say thanks for all the comments and help. I'm not a professional in any sphere though I do work in the trucking industry and try to relate anything to do with domestic water systems to the hydraulic and air systems on HGVs.

Excluding damage to pipework sticking valves and worn out diaphragms are the basis for most leaks on trucks but the advent of all this electronic wizardry has meant that many of the valves are now solenoid valves so add yet another dimension to the problem.

I am coming to the conclusion that it is a component failure within the boiler and not a general leak because up to now the water and heating system is again working fine throughout the house. Intermittent failure also leads me to this conclusion of a component failure and not a general leak.

The sticking PRV as suggested seems plausible and I'm wondering now if in the early hours of Saturday morning my leaving the inlet taps on slightly didn't "flush out" any debris causing it not to shut off properly. Then again what caused it to open slightly to trap the debris in the first place. Is the valve purely a mechanical part or solenoid operated? Does it have a diapragm or some other form a operating method? All questions that I can't answer at the moment.

It is interesting to hear that these valves can be rebuilt though if it is in the wrong, and if it is cost effective, I would probably have the whole thing replaced.

Any other suggestions would be most appreciated. In the meantime my next task is now to find a plumber or heating engineer in the Bridgwater area of Somerset who will service and repair the boiler for me.

Thanks again.

 

[alwest197]

the bits that came out of my PRV were all mechanical....just a big spring and a seal if I remember correctly.