Air entering Central Heating system

[leon_goridie]

Hi,
We moved house in the summer and obviously now are using the central heating. However I find we need to bleed the radiators every week - and when the system is on you can sometimes hear the air going through the pipes, radiators and gurgling in the pump.
I've done a search and found lots about hydrogen. I've tested for this and its not.
Its a vented system, the pump is on the flow pipe, just before the mis-position valve. The problem does not seem to happen when on the hot water only so I suspect the problem is not the pump, valve or boiler.

Can anyone provide any advice on how to do some fault finding before I call in a heating engineer to fix it. This is driving me mad now and would love to get it fixed.
Many Thanks
lg

 

[Slugbabydotcom]

Chances are that it is sucking air in through the vent

Try turning your pump down a notch or two first.
If radiators stop getting hot look at possibilty of sludge in your system.
If flushing doesnt help then the most certain cure will be to fit a de-aerator

It is possible for air to be sucked in through a failing pump, leaky rad valve or pipe joint but work on the idea of it being sucked in through the vent first.

Fitting a stop end to the vent pipe may help determine whether it is sucking in through the vent. Dont be tempted to leave it like that and dont hold me resposible for anything that happens if you do

 

[leon_goridie]

Thanks for those suggestions.
I should have said that I drained the system, and used a sludge remover to clean it out. I refilled it and used sentinel inhibitor.

It looks like the radiators have been replaced recently - so could it be a rad valve need tightening up? I can't see any signs of them leaking.
Maybe I could go round turning the radiators off 1 at a time for a couple of days each and see if it gets any better.

I'll try turning down the pump - its on 2 at the minute so will put it on to 1 for a while and see what happens.

Thanks for the help
l_g.

 

[Slugbabydotcom]

so could it be a rad valve need tightening up?

It is the packing glands that usually leak.
Take the plastic cap off. Follow the shaft down from the top of the valve and you will come to the first hexagonal nut head. This is your packing gland nut. Nip it up a little but use the right size spanner.
Sometimes you have to take the nut off completely and stuff some loosely wrapped threadtape down the slot where the nut goes. Then replace the nut to 'pack the gland'
Any leaking valves will usually have a tell tale stain running down them

 

[ricarbo]

Following Slugs suggestion of a stop end on the vent, I had a house with this problem and found a wine cork did the job. My thinking was that if the vent needed to vent it could easily blow the cork out! Obviously not an approved technique by H & S.
You know you've got this problem if you try venting the rads with the pump on, but no water comes out and air goes in, particularly at the highest rad.

 

[leon_goridie]

Thanks for the replies.

Today I went round bleeding the radiators and decided to test each one for hydrogen - using the upturned glass technique. The first few did nothing when I tested the gas - which is what happened the last time I tested.
What surprised me was that when I tested the gas from one radiator it went pop (it was a big pop nearly had to change me trousers). None of the other radiators did this

I've checked all the valves for signs of leakage - but there is none. They all look new - pegler trvs and lockshields. I tried bleeding with the pump on as well - air came out as usual - so maybe not the vent problem?

thanks again
l_g

 

[ChrisR]

You haven't told us where the vent pipe is connected yet - and the feed as well. If they're in the right places there's a blockage, so we need to know.

 

[leon_goridie]

Hi
The vent pipe goes into the loft and is above the header tank. I'm not sure about the feed - could you give me some guidance on what I sould be looking for.
Thanks again
l_g

 

[leon_goridie]

A bit more info.
I tried setting the pump to a slower speed - it was on 2 so I set it to 1. This didn't seem to solve the problem and the radiators took a lot longer to heat up - so I've put it back to 2.

The vent pipe and the feed from the header tank both seem to tee into the flow pipe just below the pump (in the airing cupboard). Its a bit difficult to tell exactly because theres hbout 6 pipes from the loft (I stuck my head through the hatch briefly).

A bit more info on what happens. The central heating and hot water comes on and all is fine. They switch off (thermostats up to temp) and when the central heating switches back on the noise of air flowing through the pump can be heard. This happens the first couple of times the central heating switches on/off in the morning and evening, but not after that. Strange.
Thanks
l_g

 

[Slugbabydotcom]

The vent pipe and the feed from the header tank both seem to tee into the flow pipe just below the pump (in the airing cupboard).

Any chance of posting a pic?

Is your boiler set to max? try turning it down a bit.

Could you try perservering with the pump down a notch thing. Its obvious that your system will take longer to heat up as the water is flowing more slowly through your system. Less vacuum from the pump will reduce the likelihod of air being drawn in whatever the source.
Is the pump old?
Is it noisy?
Are there any tell tale water marks/stains anywhere in the system?

Dont know how involved you want to get before you get someone in. I would be looking at the following to continue an investigation .

I would take the head off the pump and look to see the colours inside. You would need a 4, 5 or 6mm allen key depending on the make of pump. Turn the isolating valves off first of course.
Back core and red outer casing means that the pump is source of ingress
Quite rare but it does happen.

If both the inlet [inner] and outlet [outer] were rusty then the source is before the pump

 

[Richard Lewis]

I had a similar problem to this where there is air being drawn into the system when the heating is on but the hot water is not affected. I had a couple of towel rails installed before the summer and as part of the job the pump was replaced. The new pump is a GRUNDFOS UPS 3 and was on the factory setting of III which is the maximum. Setting the pump to II using the button on the front seems to have solved the problem. Richard