Central Heating Pressure Drop

[netview]

I have a Gloworm 30ci Combi Boiler fitted last year and have been well pleased with its performance. I have noticed a gradual pressure drop in the central heating though (0.5 bar over a few months). It currently sits at 1.1 bar

Is this normal? I don't think there are any leaks anywhere. I have also noticed some knocking in the pipes (am assuming some trapped air). Have bled (sp?) radiators, but still get knocking - could this be related?

Thanks.

 

[croydoncorgi]

Most unlikelt there's any air left in the pipes after this long. The boiler has an automatic air vent which lets it all out eventually. also, if there was air in the system, when it vented you would lose pressure. On your evidence, the rate of pressure loss is acceptably low.

When you say 'knocking' do you mean 'tick, tick' noises as the system heats up / cools down? Or 'bang, bang' noises when it first starts up from cold?

 

[htgeng]

I have a Gloworm 30ci Combi Boiler fitted last year and have been well pleased with its performance. I have noticed a gradual pressure drop in the central heating though (0.5 bar over a few months). It currently sits at 1.1 bar

Is this normal? I don't think there are any leaks anywhere. I have also noticed some knocking in the pipes (am assuming some trapped air). Have bled (sp?) radiators, but still get knocking - could this be related?

Thanks.

water can leak out of radiator valve spindles and evaporate, thus losing pressure but hard to find the cause. I wouldn't worry as long as you add a dose of inhibitor each year. There are a lot of systems out there that get topped up every few weeks and must be rusted up!

 

[netview]

Most unlikelt there's any air left in the pipes after this long. The boiler has an automatic air vent which lets it all out eventually. also, if there was air in the system, when it vented you would lose pressure. On your evidence, the rate of pressure loss is acceptably low.

When you say 'knocking' do you mean 'tick, tick' noises as the system heats up / cools down? Or 'bang, bang' noises when it first starts up from cold?

bang, bang (when the system first starts up).

 

[croydoncorgi]

Banging noises from within the boiler very soon after it fires-up USUALLY indicate a serious problem with circulation - there isn't any, so the water in the boiler actually boils, creating the 'banging'. What could be happening here is an airlock in the pipes close to the boiler, or even air / gas collecting in the boiler itself.

Does it make the noise only on CH? or in hot water mode too?

Is this boiler in a flat? multi-storey house?

As a first step, it would be worth checking that the dustcap on the auto air vent inside the boiler is actually LOOSE - it should be, otherwise the vent won't work! You're looking for a small brass cylinder 40 - 50mm high with a black or red plastic dustcap

 

[netview]

Banging noises from within the boiler very soon after it fires-up USUALLY indicate a serious problem with circulation - there isn't any, so the water in the boiler actually boils, creating the 'banging'. What could be happening here is an airlock in the pipes close to the boiler, or even air / gas collecting in the boiler itself.

Does it make the noise only on CH? or in hot water mode too?

Is this boiler in a flat? multi-storey house?

As a first step, it would be worth checking that the dustcap on the auto air vent inside the boiler is actually LOOSE - it should be, otherwise the vent won't work! You're looking for a small brass cylinder 40 - 50mm high with a black or red plastic dustcap

The knocking only happens on CH, and in the morning when the heating first comes on. The boiler is in a two storey house on the ground floor. The knocking always sounds like it is coming from the pipes in the floor space above the boiler.

I have checked the valve, and it is loose. I also noticed an unusually high gas bill last time - not sure if this could be related. The pressure in the boiler dropped by another 0.1 bar today - now at 1 bar.

The radiators do get hot though, and there is circulation.

 

[croydoncorgi]

In a 2-storey house, you only need about .5 bar static head to get water up to the 1st floor, so chances are the boiler will stop due to low pressure before the rads upstairs empty! But you do need to discover where the pressure is going. What worries me immediately is that the 'bangs' are causing blips of high pressure which lift the pressure relief valve and release water down the discharge pipe. Is there any evidence of water coming out of a pipe on the wall outside, below the boiler?

Since the bang problem only happens after the boiler has been off for a while and got fully cold, I'm beginning to wonder if the pump is sticking then freeing itself after / when the boiler overheats and bangs. The way to check is turn the timer off, and then turn the CH on manually in the morning, and note the sequence of noises as it starts up. You should hear the pump first, then the flue fan, then the ignition (tick,tick. tick) followed by the burner flame appearing and the temperature indication on the LCD display rising. If the flame comes on but the water temperature stays low until the bang(s) happen, then it's probably a jamming pump. Fixing it will require draining the boiler. Also - why did it jam? Corrosion? Debris from the rads? Tends to point to installation without first flushing the rads (I assume it was not a complete new system last year) or no corrosion inhibitor in the system. Tricky problem - but my first suggestion is to call the original installer back. It could also be a faulty pump - warranty repair - but it will require a qualified engineer to diagnose it.

 

[netview]

Thanks for the reply. There is no water from the discharge pipe outside. I will check for the startup noises you mention and will let you know if there is anything that sounds odd. Otherwise I will have to get the installer back for a look!

Thanks again for your help.