Hi, to anyone who can help me :-)

I have a Baxi Bahama 100 combi boiler. Just recently, it has developed a crummy fault: When the Heating is running, the pressure rises consitently until it reaches 3 bars and I turn it off (as I loose my bottle).

When it all cools down, the pressure returns to about 1.2 in the green.

No matter how LOW I initially set the pressure, this still happens when I try the heating.

Also, I should point out that this only happens when the heating is running. There is no pressure movement when the boiler is dorment, and the hot water feature works fine (with a little pressure drop whilst on).

I have monitored the heating flow and return pipes on the boiler, and can say that it does not take very long at all for the heating return pipe to get hot, indicating that there isn't a blockage in the external piping. (Also, ALL of the radiators get hot pretty quickly).

That just about covers it, so can anyone throw me some ideas please?

I will be even more grateful than that Blunkett fella.

Dawse, May 2005

Thank you d.. for this advice you have saved me calling out an engineer.

"just bleeding the radiators should be fine and the boiler should vent itself via the auto air vent .. with the system cold the pressure on the boiler should be about 1 bar and should only rise to 2 to 2 1/2 bar but just keep an eye on it. i hope it behaves itself good luck !!

d.."
Thanks again.
J Young.

J Young, January 2013

the boilers turns it self off after about 15 seconds of running on hot water also on heating .

mark ac, August 2009

you need a new expansion vessel

stu, September 2008

the expansion vessel is f***. this is a common fault on this boiler and if you replace the vessel all should be ok. But do it quick because the vessel will leak on the pcb's , and they will short out(this will cost you about £200 plus!!!)Vessel about £75 plus fitting

David Walters, October 2005

Magic ... thanks again d.. :-)

Dawse, May 2005

just bleeding the radiators should be fine and the boiler should vent itself via the auto air vent .. with the system cold the pressure on the boiler should be about 1 bar and should only rise to 2 to 2 1/2 bar but just keep an eye on it. i hope it behaves itself good luck !!

d.., May 2005

Well, did as you said and charged the EV to 1bar with a drain valve open and no boiler pressure reading. (Incidentally, before I started recharging, the pressure reading on the Expansion Vessel was 0! )

Anyway, the expansion vessel does seem to be holding the charge and I've just had the heating running full on. The pressure rose only very slowly this time (was pretty fast b4).

The pressure still rose pretty high (almost red), but turning the thermostat down to a reasonable setting clicked the heating off. So, dare I say it... I think we've cracked it for now. Thank you so much.

I will keep an eye on it to see if things change. Pleeeease no!

---------------

Quick question b4 you get fed up of me... Do I need to do anything other than bleeding radiators after draining the boiler so much and replenishing? (A lot of water came out the boiler whilst I recharged the EV)

I know there is an "automatic air valve" on the top. Does this let out any air that may be in the boiler itself without my help?

Basically, the idea of air in the boiler, or how to deal with it after draining down is something I'm generally not sure about. I've heard a lot about "venting the system", but I'm not quite sure what is meant. Does it just do it by itself with this auto air valve on the top?

Thanks again d...

I really do appreciate your very generous guidance, and the world is a better place :-)

Dawse, May 2005

just make sure the pressure relief valve doesn't drip afterwards or you will keep losing pressure and will have to replace it

d.., May 2005

Thanks D, gonna try it now. I'll let you know

Dawse, May 2005

you can sometimes get a some water in there so don't worry try recharging it 1st.. what you need to do is open a drain valve on the system and release the pressure.now use your footpump to repressure it but you must keep the drain point open whilst pumping up the vessel,when the footpump reads 1bar close the drain point and refill the sytem .. hope that helps

d.., May 2005

Thanks a million for your reply.

Do you mean the expansion vessel?

I have a full copy of the service manual, but it just tells me that the expansion vessel should be pressurised to 1bar (10lb/in2). No instructions... Although I have also read somewhere that it can be recharged with a bicycle pump? (I could well be wrong)

Breaking news: I just put a pressure gauge on the valve on the front of the expansion vessel and water came out. I was expecting to get air, so does this mean the diaphram inside has broken? If not I'll shut up, and be very grateful for any further instruction that you can give me...

Thanks again!

Dawse, May 2005

it sounds like your pressure vessel on the boiler needs recharging the details on how to do this may be in the instructions if not i'll talk you through it..

d.., May 2005