I have a Baxi Combi 105 HE Boiler. I have recently noticed the pressure gauge dropping to around 0.5 bar or less but with no apparent loss in performance on either the central heating or hot water. However, in the last 2 weeks the water flow on my shower has often failed with the "low pressure" light being illuminated. I am assuming the problem is the low boiler pressure and not the shower and that I therefore need to increase the boiler pressure.

Can anyone please help

Tony S., May 2010

Thanks to all.

I sorted the boiler and a plumber has condemned my shower to the bin - it was a very old version of the mira sport 8.5kw.

Just bought a new shower today so job done.

Cheers.

Tony S, May 2010

Regarding loss of system pressure this can either be external ie rads and v/vs or internal of your boiler.Loss on your external side should be evident carefully inspect as far as possible all your pipe runs,rads and v/vs at suspect points leave some cardboard to highlight drips. Inside your boiler you have an expansion vessel which is a 6-10 ltr pressed steel tank which contains a slack rubber diaphram.One side of the diaphram is charged with air to 0.8-1.0bar as your boiler is warming up the expanding water enters the tank acting against the diaphram displacing the diaphram and compressing the air on the other side by the volume of heated water produced.If the standing charge pressure leaks away over time the system water fills the space and thus there will be an apparent loss due to the mass off water now in a slightly bigger system volume. Recharging is not difficult job download your manual from Baxi which will show you your valve station and duties ,you initial charge pressure and your top-up hose which you must have as your boiler does not have a built in one. This isn't rocket science.

Guytawe, May 2010

Thanks very much Mivy and Guytawe.

I am not aware of any leaking radiators or leaks elsewhere on the system. Is it possible for the pressure to drop off gradually and not be due to a water leak?

All taps in the house have good pressure.

Thanks for the info on the shower issue not being related to the boiler. I will check the intake filter for muck.

The bottom of the boiler has about 5 or 6 valves from memory. Is there a sure fire way that I can identify the correct one to top up the system. I gather it is the cold water intake but how does a novice like me make certain I get the right one?

Tony S., May 2010

2 separate issues

if the pressure gauge keeps falling on the boiler, you need to check this out, as this should be a sealed system and if the pressure drops over a short period of time, it would suggest you have a leak on one of the radiators or even central heating pipework. Can top up using fulling loop (steel house at bottom of boiler)

As for shower, clean filter for water intake.

Do you have low pressure on all the taps in your house?? If so check stop clock is open enough and if it is it may be worth contacting water board as you could have an old supply to house which has now become furred thus reducing water pressure, but water board could confirm this.

Mivy Gas Safe, May 2010

These 2 problems are not related,if you have a light on your shower indicating low pressure I would conclude you have an electric shower if so then check your cold water supply or shower inlet filter.You state that there is not a fall-off in hot water so at present your low pressure is not affecting or shuting down the boiler.Just open your top-up valve/valves and lift the boiler when cold to 1bar or 1.5bar hot.This pressure is only the water pressure in your rads nothing to do with your shower in any respect.

Guytawe, May 2010