Blocked vent pipe in open system?

[Unklian]

Hi Again.

Apologies for the crappy sketch!

My central heating system has become noisy.
It happens when the hot water valve opens.
The pump starts and I can hear water running near the coil in the cylinder.
It sounds like there is a load of air trapped.
It has only happened recently.
As far as I can guess, any air bubbles in the system should go up the
vent pipe at (A). The system should then be replenished from the header tank via point (B)

After reading a recent post, it was suggested the vent pipe could be blocked with "set" sediment / corrosion. Presumably, there is then nowhere for the air to go other than to circulate round the system to be eventually bled from the radiators.

I have tried to make the system pump over (By removing the valve heads, having the system call for heat so the pump starts, then manually closing the valves briefly) but to no avail.

I was thinking of cutting pipe (A) just above the 22mm coil pipe and replacing the 15mm overflow pipe.

Any suggestions / help / advice?

Cheers.

Ian.

 

[slapper]

You need to get a Plumber in to look at your system.If your drawing is anything to go by, I wouldnt risk endangering people by you messing with it.

 

[Unklian]

The system is quite old,

The reason for placing the valves where they are is due to the fact
that it was pumped heating, gravity water originally, with DHW temperature controlled just by the boiler temperature.

By having the valves fitted and running the system "properly", gas
bills were reduced by 30%.

I'm aware the valves are by no means in the best place.

(And we have more than one radiator)

It normally works very well, the rushing water / air noise is new though.

Ian.

 

[transam]

as you are probably aware , the pump situated on the return , means the system is under a negative pressure , the water is being sucked around the system , not forced or pumped around . There may be a quick answer but it depends on wether your boiler has an overheat stat.

 

[Unklian]

Yes, the boiler DOES have an overheat stat.

Ian.

 

[Goldspoon]

Your vent should be 22mm and not 15mm. So your suggestion of replacing the 15mm is a good one. Then you can see if the old stuff was blocked.

Bear in mind your old pipework may be imperial rather than metric so you may need to use a suitable adaptor.

 

[Unklian]

Before cutting the pipe above (A) to replace it,
I decided to check if it was blocked by blowing down it.

As I did this, I could see the level of water in the header tank go up.

Hurrah!

Releasing the pressure allowed the water back up the vent pipe in a rush.

Bringing with it a large lump of air.

System now silent again.

My only thought is that the long (4m) horizontal pipe in the loft before the
rise up and over the header tank was somehow trapping air.

Come Summer, I think I'll re-position the header tank straight above where the feed / vent pipes enter the loft space rather than 4m to one side.

Cheers for any advice given.

Ian.

 

[Goldspoon]

My only thought is that the long (4m) horizontal pipe in the loft before the
rise up and over the header tank was somehow trapping air.


Ian.

I think you could well be correct