Glow worm boiler problems

[Londi]

got a glow worm boiler thats about 10 years old that during the summer dosent need much repressurising at all,once every now and again.

since the cold snap the pressure when the boiler is not on (ie overnight) drops to more or less zero. if you repressurise it to say 1 bar when the heating kicks in it goes round to between 3 and 4 bar and starts to eject water from the overflow pipe underneath.

when it settles down again it rests at about 3 bar then same again when left overnight.is this a boiler fault or a fault with the heating system itself?

any help apprecated before i start calling people.

 

[weareleeds]

Expansion vessel needs repressurising

 

[captain_pugwash]

sounds like it could be the expansion vessel has stopped working - this is usually built into the back of the boiler unless you have an external one fitted. If in the boiler then it's usually right at the back and is a bit like a hot water bottle. It's job is to absorb the increase in pressure that occurs when the water heats up. If it stops working then the pressure guage on the boiler will show the big rise in pressure and then the pressure relief valve (prv) is there to stop the system blowing a leak by releasing out the pressure usually at 3 bar. The problem with prv's is that once the have cut in they alomost always seem to leak thereafter - my Glow Worm has now had 3 in just 2 years.

It could be that the expansation vessel has lost its pressure. If you are able to take the cover off the boiler and then look in the top by the flue you should see a valve like on a car tyre - in fact the way to test and re-pressurise is to attach a car tyre pump with a pressure guage and then pump it up to 1 to 1.5 bar.

The setting of the pressure on the EV has to be done with the boiler drained down - use the drain valve (and a hose into a bucket) rather than the lever on the prv as this will only make the prv leak worse in my experience.

If the expansion vessel is okay then there must be another reason for the rise in pressure - something must be blocked somewhere. Occassionally the small tube that connects the water flow from the boiler to the expansion vessel can get blocked - this can be quite tricky to get at on some boilers - usually it's found going from the back of the pump somewhere inside the boiler to the bottom of the expansion vessel.

If the water is black and lots of bits of sooty stuff come out when you drain it this could point to a blockage. You could then use Fernox boiler restorer to clear the boiler out. I use a mastic gun with a tube a circlip to pump it into the filling loop connector.

If the EV is okay and pipe is clear then I'm stumped. You may want to try running the boiler at a lower temperature - say around 60 degrees instead of its maximum to see if that helps.

good luck

 

[chrishutt]

This is coveed in the sticky reference topic.