Is this right - pressure increasing on boiler when heating?

[curvy1977]

Hi, I am going to get a gas engineer out as I have no hot water (runs hot/cold and the flame drops and goes out altogether whilst the water runs) but I'm curious about the pressure and thought I'd ask out of curiosity.

The boiler is a Potterton Performa 24. I only moved here in May, the previous owner said family serviced it so I had it serviced as a matter of priority and was told it looked very clean and in good condition.

After I had a radiator off in a bedroom for DIY, I added water to the system bringing the pressure up to about 1.5 bar. But I noticed after that that if the heating was on for longer than 15 mins or so the pressure steadily increases until it's in the "red" and over 3 bar. The boiler seems to kick in and off again whenever it's supposed to be heating. The radaitors do get hot fairly quickly though.

Is this right?

 

[flameport]

The pressure will increase when heated, as the heat causes the water to expand.
Any expansion is normally taken up by the expansion vessel.

However in your case the pressure is increasing far too much, so it is likely the expansion vessel is either empty or has failed, so will require refilling or replacement.
Info here: //www.diynot.com/forums/viewtopic.php?p=251090#251090

If the pressure increases over 3 bar, a relief valve should operate and let some of the water out - this will also mean the pressure will drop to almost nothing when the system has cooled.
If this isn't happening the valve will also need to be replaced, and if it has seized shut, the system is dangerous until the valve is fixed.

 

[curvy1977]

Thanks and poo!

Whilst I don't tend to put the heating on for longer than 15 mins at a time (I'm trying to avoid using the heating much) there clearly have been times when it's been over 3 bar (red line starts at 2.5 bar) yet the current pressure is between 1 and 1.5 bar so it can't have lost much...the implication being that the safety device is not kicking in.

I guess it's a good thing that I'll be calling a gas man in asap!

As a matter of interest, is there any way of me telling if this has been a problem which developed recently or if it was a long term thing? I was planning on calling the chap who serviced the boiler last May (also fitted a cooker, removed a rickety looking gas fire and gas pipe from a bedroom wall for me) and whilst he was recommended to me, I'm wondering whether he should or could have picked any of this up when he serviced it.

 

[Agile]

Thats an interesting question!

The plain fact is that all British Gas and probably 80% of independents would not have picked it up and my interpretation of that situation is that its not something which is checked by the majority of engineers.

When I do a service, I ask a lot of questions of the users to determine if there are any issues which I need to be aware of.

I do not specifically check the expansion vessel air pressure unless made aware of a likely problem. BUT I do run the heating for about 10 minutes whilst monitoring the system pressure increase and if there was an expansion problem then I would become aware of it from that.

Running the heating like that also shows up other possible faults like cycling and incorrect heating power settings.

For the gas guys I also check the min/max and ignition gas pressures and the CH power setting.

Tony Glazier

 

[BARNY78BG]

Thats an interesting question!

The plain fact is that all British Gas and probably 80% of independents would not have picked it up and my interpretation of that situation is that its not something which is checked by the majority of engineers.

Tony Glazier[/quote
Hey Tony, look mate, i've read a lot of your texts since joining ths site and feel you are indeed a very experienced, knowledgable engineer and take in a lot of what you advise but....... on saying that, i've also read your jibes on bg engineers????? as with every company you have your top and bottom engineers, there is a range. i feel you have a gripe with bg and portray all thier engineers as the same as one of your earlier threads posed that when all experienced engineers supposidly left the company then there were only the incompetent ones left!!!!(not your exact words i know.) you are so wrong mate!!when ever i and many of my colleagues go to jobs we indeed do look for symptons of a faulkty system, including expansion vessel problems. i do rate you but feel that you are painting us with the naughty brush, and quite frankly am quite cheesed at it!

 

[curvy1977]

Just to keep things tidy, I'm reporting back. Hot water issue was caused by the heat exchanger which has been replaced and the pressure issue by the expansion vessel, which will be replaced too.

Thanks for the help and advice.