Baxi platinum 33 losing pressure heating only?

[Ruggers]

My 8 year old baxi platinum is losing pressure when the central heating is running but holds for months with the domestic water. I have eliminated leaking pipes by closing flow and return valves, I have had a bag on the pressure relief pipe and it collects nothing until i run my central heating, then i get about 1 cup of water and i lose pressure on the boiler.

Can anyone tell me why it is only leaking via the PRV on heating but not on water and what i need to fix this?

 

[ianmcd]

You need to re-pressurise the expansion vessel tells you how to in the wiki on here but follow all the steps dont just pick which ones you want to or it wont work

 

[bernardgreen]

http://www.baxi.co.uk/information-and-advice/heating-advice/water-pressure-hints-and-tips.htm

If the pressure goes above 3.0 bar, the safety pressure valve in the boiler will operate and you may see water coming out of the pressure relief valve, which is usually on an outside wall near where the boiler is installed.

Pressure in the radiator system will increase with temperature, either the PRV is letting out at a lower pressure than it should or the pressure is going too high when the central heating is running

 

[denso13]

//www.diynot.com/diy/threads/faqs.37170/#post-251090

 

[Ruggers]

Thanks guys. The prv is definitely passing as ive got a clear bag tied on the overflow and it only fills if i use central heating but fine for a month on hot water only.
Not sure why that is?
Im familiar with most components in the boiler but not 100% on the pressure vessel. Is this something that requires half air in to function or is the air just a means of testing? Its never been topped up in 8 years from new.

 

[St0rmer66]

The PRV is NOT "passing", it's doing it's job.

 

[DP]

Usually when it gets to that stage, it is often due to lack of proper care and attention. Would not be surprised if the diverter is/ will be weeping some time soon

 

[Ruggers]

I never said it wasn't doing it's job i just mean as it is now when i run the central heating it passes or does its job for whatever reason. I was wondering what type of fault may cause a boiler to function fine on hot water but creates excess pressure when the central heating is ran.
It will need identified before the PRV is renewed otherwise the new one will just be cracked open and then pass again. I was wondering if i turn the central heating side right down on the boiler and run the heating and see if it does the same to eliminate the temp sensor being broken and making it run too hot increasing the pressure?

 

[St0rmer66]

It's just a flat expansion vessel, as was already mentioned. Very routine job. If the boiler has been serviced with any kind of regularity it would have been picked up then.

 

[ianmcd]

when you run your HW you are only heating the volume of water within your boiler, when you run the CH you are heating all the water in the complete system hence why you only have an expansion problem when heating is on

 

[kevplumb]

It's just a flat expansion vessel, as was already mentioned. Very routine job. If the boiler has been serviced with any kind of regularity it would have been picked up then.

well it obviously hasn't been
OP get a bike pump drop the pressure and pump till you get 1.5 bar

 

[hertsboilers]

It's just a flat expansion vessel, as was already mentioned. Very routine job. If the boiler has been serviced with any kind of regularity it would have been picked up then.

Don’t think even big boiler insurance companies like British Gas, HomeServe or Corgi will do expansion vessel recharge while “servicing” their customer's boilers. But the customers are covered for repairs. More and more I have seen expansion vessels are flat. Lol.

 

[kevplumb]

i hear ya brother
its not right but its the way it is

 

[ianmcd]

unfortunately I have worked as a manager with a few large so called service providers and its astonishing how many of their so called engineers haven't a clue how to recharge an expansion vessel, most press the Shraeder valve and if they feel any water then it needs replaced according to them

 

[oilboffin]

Oh yes some haven't heard of condensation