Low pressure in expansion tank

JohnBristol · Apr 11, 2013

Hi there,

I am after some advice on if I can fix this myself. I am far from a DIY master but I can handle the basics.

Background:

Boiler: Unsure I can't see any markings on the front just a white panel and some stickers from when it has been serviced by local companies.
Water tank: Megaflo
Red expansion tank

I noticed a few of our radiators at home were not getting very hot so I bled them all and on the last 2 which happened to be at the top of the house they never fully bled, i.e. no water came out. I tighten them anyway did not think much more about it. Then I noticed the boiler(in kitchen) started turning itself off after a few minutes, if I reset it it would stay on for a couple of minutes then turn off. I thought something was wrong so went to the airing cupboard with the water tank and expansion tank in. I noticed I could not hear anything from the pump so I thought it was broken, I pressed what looked like a reset button but I think is now a cycle between modes button and it made some noise and when I reset again the boiler fired and stay on and radiators got hot. This had been happening periodically for a couple of weeks and I have now notice that the pressure gauge below the expansion tank is between 0.1-0.2bar when cold, when the pump is on high and the boiler stays on it goes initially to 0 but slowly builds up to 0.5bar

Based on my research I think I need to repressurise the expansion tank. I am happy to do this but before I start doing something really silly I thought it would be an idea to put this out there and to see if I can fix this myself or if I need to get a professional in?

Any help would be greatly appreciated.

snowhead · Apr 11, 2013

What you can see on the gauge is the system pressure, not the pressure in the expansion vessel.

JohnBristol · Apr 11, 2013

I thought it might be system pressure but could not see another gauge for the expansion tank so was not sure.

The other thing I read about was potentially needing to top the system up with water. I have found what looks like the right thing. A flexible metal braided hose goes into the pipework near the gauge. I have never touched this before and it looks like the tap is open and has always been open. My understanding was it should not be then turned on when you need to top the system up. It is also already connected and from what I have seen it is normally left disconnected

Reltub · Apr 11, 2013

When you bled the radiators you would of depressurised the system. All you need to do is repressurise it using that hose to around 1.5bar.

mutley racers · Apr 11, 2013

simples

JohnBristol · Apr 11, 2013

But as I mentioned the hose is already attached and seems to be open. Unless I have missed another tap somewhere that is stopping the flow of water.

The tap I have found is next to the hose end furthest from the gauge.

Simon F · Apr 11, 2013

Hello John, welcome to the forum.
It might help to post some pictures if you are not to sure.

a good filling loop will have a tap at both ends.
the tap will be most likely be open when in line with the pipe and closed when at 90 degrees to the pipe.
the loop should be left unconnected, but not likely.

JohnBristol · Apr 11, 2013

Thanks for the help everyone.

while trying to take some photos I also found the other tap. System now repressurised 🙂

boiler fired up first time afterwards