Glow worm boiler at 0.3 bar

[karflips33]

Our boiler pressure has gone down to 0.3 bar, we have tried turning the blue water knob underneath (usually works), there is no sound of rushing water like there usually is, and the net effect of turning the knob is zero.

We have done a bit of research and discovered that the expansion vessel valve can be used to pump up the pressure again. With great difficulty we got the cap off the expansion vessel and attached a bike pump, we gave 20 or so pumps and turned the boiler back on, but the pressure had only shifted from 0.3 to 0.4 - we cannot seem to get it any higher by pumping air in.

We tested the valve, and there was a sound of escaping air, so we guess our diaphragm is not ruptured.

We don't want to do much else because we do not want to destroy our expansion vessel or damage the boiler in any other way.

We were wondering if we've missed any other vital steps - in another post we read that you need to depressurise the main system first, but we have no idea how to do that. Howe much air do you need to pump in with the bicycle pump for the expansion vessel to regain ideal pressure?

[<me9]

With your main system down to 0.3 bar it's near enough depressurised. Opening a drain c*ck, or the PRV will get that last bit down. 0.7 bar (use a tyre pressure guage) should be about right for the pressure vessel with low or no pressure in the water system.

You should have a filling loop or valve for topping up the water side.

I suggest you first look at the sealed system FAQ at

[karflips33]

Thanks for your reply.

We have a filling loop, usually when we turn it on, there is the sound of rushing water, and the pressure goes back up into the ideal range. At the moment when we operate the filling loop, nothing happens at all, and there is no sound of rushing water.

We were wondering if this is symptomatic of a broken filling loop, or just a side effect of something else.

We have a car tyre pump with gauge, but we're too scared to attach it to the expansion vessel value, in case it over-inflates the vessel and ruins it. Also, the gauge on the car tyre gauge goes up to 250 psi

- much more than the 7 psi needed for the expansion vessel, so it's not a very good gauge of how much pressure is in the vessel - attaching the pump to the vessel valve barely moves the needle.

Also, is using a bicycle pump a practical way to repressurize the expansion vessel? We pumped away for a while, but had no effect when we switched the boiler back on??? How much pumping should be necessary?

[Roger Mills]

There should be *two* valves/taps on the filling loop. Are they both turned on? [When you're not topping up the system the filling loop's flexible pipe should be disconnected - so it needs a valve at the mains end to stop water pouring out when the pipe is removed and, similarly, another at the heating system end which remains with the system to prevent *that* emptying]

So you can test the filling loop by disconnecting the hose. When you open the valve at the mains end you should get mains water coming out (so use a bucket in which to catch it!). Likewise when you open the other valve, heating water should come out - so this is a good way of making sure that the system is unpressurised before you pump up the air in the expansion vessel.

You can use a bicycle pump if you wish, but you *must* be able to measure the pressure when you've done it - no-one can tell you how many strokes of the pump are needed! The usual charge pressure is about 0.7 bar - which is

10psi not 7psi. If the gauge on your car pump doesn't provide sufficient discrimination, buy a cheap pressure gauge such as from Halfords.

[karflips33]

Thanks for your input - in the end, it turned out to be debris stuck in the filling loop valve.

[adder1969]

The water pressure in the system and the air pressure in the vessel are separate items. Air compresses into the limited space. If you pump it up too much you can damage it. You should set it to the manufactures recommended setting.

Sounds like the mains water has failed or been switched off or the filling loop valve is either still closed or the non-return valve is stuck. You supposed to disconnect the fillign loop once you've filled it. The next thing is to work out why the system has depressurised - usually it means a leak somewhere and it can be tiny (until your ceiling falls in)

[<me9]

Not true, there should be a double check valve at the boiiler inlet to prevent the system contents from backflowing into the mains.

Did I say 7psi? I meant 0.7 bar, which you rightly say is 10psi (ish).

A car pressure guage should be able to measure that, or it in't likely to be very much use for tyres.

[Roger Mills]

I stand corrected! Actually, I did wonder after I had written it whether there was perhaps a non-return valve rather than a manual tap at the system end. [One day I'll convert my system to pressurised, then I'll have first-hand experience! >> We have a car tyre pump with gauge, but we're too scared to attach

No, it was the OP who said it.

[David Hansen]

On Mon, 07 Jan 2008 16:52:22 GMT someone who may be wrote this:-

The double check valve is slightly better placed on the mains side, to prevent the rather remote possibility of back siphonage via the filling loop. It also allows draining/relieving pressure via the filling loop. The disadvantage is that it allows those with inquisitive fingers to turn an easy to turn valve and allow hot water out under pressure.