Water discharging from the loft vent pipe as CH turns off?

[Markw996]

Hi,
I have just moved into my first home, a 2 bed semi-detatched and as the title says I have a very noisy central heating system.

As it comes on I get lots of bubbling / gurgling noises that last about 10 seconds and seem to originate from either the upstairs radiators or the airing cupboard.

Also as the central heating clicks off it sounds like someone emptying a bucket of water up in the loft right above my bedroom (very worrying the first time it happened!).
I traced the loft noise to the expansion tank in the loft where, as the heating clicks off, I am getting about half a litre of water discharging from the vent pipe back into the tank.

The system is open vented circa 1992 and I take the vent pipe to be the one that rises about a foot above the tank, then bends in a U shape back down into the tank.

I've had breif discussions with a plumber friend and he says it could be the boiler thermostat?!? but I suspect it is more likely to be air in the system somewhere (although I am certainly not clued up on central heating systems) as I did have to bleed a lot of air from by bathroom radiator when I first moved into the house due to it being very cold at the top.

Just to summarise:
I have 2 tanks in my loft and the problem is relating to the smaller tank which does the central heating.
My boiler is located in a downstairs cupboard.
My airing cupboard is upstairs and contains an immersion tank, pump, and a motorised valve of some sort.

I hope someone can help as the noises wake me up in the mornings and annoy the hell out of me in the evenings! (

Many Thanks,
Mark.

 

[jase158]

Hi, When does it happen? (after heating has been on for an hour,as soon as heating comes on, when hot water in use i.e.)
Where do you live?

 

[kimbo]

Like all these jobs it is beter if you are there to make a good judgement however I would be thinking possibly pumping over the vent possibly pump set too fast, air being dragged in through the vent. The vent and cold fill in wrong place should be 150mm apart etc. More information would be good

 

[WHPES]

Easiest way to fix - convert to sealed system. The hours spent on determining the problem which may not be easily fixable would best be put to converting it over.

Do not leave it. Every time you draw air in will encourage rapid corrosion of the radiators, or lose water through the overflow will dilute any rust inhibitor.

 

[wards]

blockage in circs,find blockage in system and rectify,or call in a professional to carry out the work for you.

 

[stevetheplumber]

if its only a small amount of water each time it shuts of raising the vent or oversizing a section around the water line can stop this
but id try running pump down one notch first

 

[yorkieplumber]

Check pipework is correct in cylinder cuboard ie cold feed and vent, the fitting of a airjec is usually a good solution, converting system into a sealed system is rather a drastic measure.

 

[SafeGasInstall]

I might be wrong but I thing you need to get a auto bypass fitted ,if the fault is just after heating goes of ,but if it happens when working let say 1h then I think is the cold feed might be blocked

 

[Markw996]

Thanks for all the suggestions.

I have just taken some photos of the pipework inside my airing cupboard in case anyone can see anything wrong? (sorry but I don't know how to rotate them)



I've also turned the pump down to minimum (it was set on about 2 of 4) and I'll see if it gets better or worse.

The easiest solution seems to raise the vent pipe a bit higher, I may give that a go this weekend as it's a pretty simple job.

Thanks,
Mark.

 

[tamz]

Could do with a bypass valve or even a 15mm gate valve fitted. (on 15mm pipe 1st tee below pump). It is not really needed.
Turning the pump down should help. Also drop the water level in the F&E tank a bit by bending the arm of the ballcock down.

 

[Markw996]

Could do with a bypass valve or even a 15mm gate valve fitted. (on 15mm pipe 1st tee below pump). It is not really needed.
Turning the pump down should help. Also drop the water level in the F&E tank a bit by bending the arm of the ballcock down.

Thanks tamz, so I'll raise the vent pipe by about 10" and drop the water level in the tank by bending the arm and see if the problem goes away.

The vent and cold fill in wrong place should be 150mm apart etc. More information would be good

How would I tell which is the cold fill? Are you refering to the pipes in the loft? If so can you explain what I should be checking?

Unfortunately I don't have any more information at the moment, it does seem worse first thing in the morning though, maybe for the first hour of operation... and less so last thing at night if that helps? I'll have to monitor it for a few days to see if I can give better detail.

Thanks,
Mark

 

[tamz]

It is probably more pump related than anything else.
The system looks piped ok. Vent and feed max 150mm apart so it looks fine. Keep the pump on the lowest setting that it works on (simplified that one a bit).

Could be a bit sludge related.
What colour is the water if you bleed a rad?

 

[Plumbcrazy56]

I have rotated the pictures for you.

And as already stated, I would look for a blockage in the cold feed at the tee indicated by the X

 

[Markw996]

Could be a bit sludge related.
What colour is the water if you bleed a rad?

It was definitely quieter this morning with the pump on the lowest setting, it didn't even wake me up!

As for the rads, all give clear water except the one in my bedroom which is BLACK water

I have rotated the pictures for you

Thanks, it was starting to strain my neck!

Could I check for a blockage by removing the pump & rodding the vertical pipe? Or would I need to cut out the tee and replace it anyway?

Thanks,
Mark

 

[Plumbcrazy56]

Try draining the system without turning off the water to the expansion tank. if it drains but the tank stays full then you definately have a blockage.