Back Boiler Loud Gurgling Noises

[HWPipe]

Hi all.
I have an oil fired central heating system that also has a fireplace with a back boiler plumbed into it. The system has a dual coil copper cylinder with the oil side heating one coil and the back boiler the other. There is a pipe stat on the back boiler supply to the copper cylinder which starts a circulating pump which then transfers heat to the central heating radiators when the desired temperature is achieved. There are also three non-return valves in the system. A standard enough system in other words.

My problem is this - the heating has been running with no apparent problems for years but recently when the back boiler circulating pump cuts in I can hear loud gurgling noises from the copper cylinder. It sounds like there is an amount of air in the system and that the water is just trickling through the back boiler coil on the tank. When the thermo siphon is operating everything is quiet and heat is being transfered from the back boiler to the copper cylinder. When the oilfired heating circ pump is operating everything is quiet aswell.

The system doesn’t appear to be losing any water as I have tied up the ball cock in the expansion tank and the level has not dropped over a week, even though one of the radiators does need to be bled frequently.
I have had the back boiler circ pump running for long periods with no fire lit to try and work any air in the system out of it with no success.
I have had the thermo siphon circuit flushed and have been told that there is a no problem with the flow through it.
I also get plenty of domestic hot water when the fire is lit.
The radiators do get warm throughout the house when the back boiler circ pump is dumping the heat to them, but it is when the back boiler circ pump is running that I get this loud gurgling sound.

If any of you experts out there have any light to shed on this it would be much appreciated.

 

[stevetheplumber]

if your bleeding a rad with the ballvalve tied up and the level doesnt drop youve got a blocked cold feed

 

[Pipes Plumbing]

if your bleeding a rad with the ballvalve tied up and the level doesnt drop youve got a blocked cold feed

I agree! Try draining some water from the system and see if the level drops immediately. If not it's Do Not Use until the blocked bit is chopped out and changed.

 

[HWPipe]

if your bleeding a rad with the ballvalve tied up and the level doesnt drop youve got a blocked cold feed

Sorry I didn't put that too well ......I didn't bleed the rad whilst the ballcock was tied up. The rad requires to be bled whilst the heating is in service under normal conditions. The cold feed has been proved to be clear as the system has been drained down to change the copper cylinder and changing the cylinder isn't the cause of this problem as the system was making the noise before it was changed.

 

[HWPipe]

I agree! Try draining some water from the system and see if the level drops immediately. If not it's Do Not Use until the blocked bit is chopped out and changed.

Thanks for that but as I said the cold feed is clear as the system has been drained down successfully.

 

[Pipes Plumbing]

Thanks for that but as I said the cold feed is clear as the system has been drained down successfully.

Noises that aren't from vibration or expansion / contraction are usually either from Air, Velocity or debris.
Have you:
- Vented the solid fuel coil (at the top coil union) to make sure there's not a partial air lock in there getting whacked around by the pump.
- Made sure that the pump hasn't been turned up from it's original setting and that none of the rads have been shut down or opened up.
- Made sure that there's not a load of flaky black rubbish whizzing round in the system.

Without actually seeing / hearing it, it's kind of tricky to understand exactly what it's doing...

 

[HWPipe]

Noises that aren't from vibration or expansion / contraction are usually either from Air, Velocity or debris.
Have you:
- Vented the solid fuel coil (at the top coil union) to make sure there's not a partial air lock in there getting whacked around by the pump.
- Made sure that the pump hasn't been turned up from it's original setting and that none of the rads have been shut down or opened up.
- Made sure that there's not a load of flaky black rubbish whizzing round in the system.

Without actually seeing / hearing it, it's kind of tricky to understand exactly what it's doing...

It is not Vibration or expansion/contraction.
I have tried to vent the solid fuel coil at the top union and I am only getting water also the system is vented from this union so I reckon any air should make it's way out through the vent (but I know with air this is not always the case).
The pump hasn't been changed from original setting.
The rads are the same as they have always been.
The back boiler thermo siphon circuit has been flushed and there was not much muck in it at all.
You are right though it is a tricky one and I am looking at it and hearing it lol.
What I do not understand though is how it has just developed. It really does sound like it is air. Where has the air suddenly come from? --- A leak? Then why has the water level not dropped in the expansion tank.

 

[Reg Man]

Is the open vent pipe clear?

 

[HWPipe]

Yeh the vent has been proven clear

 

[diamondgas]

Could be nitrogen? When was the system last drained? When was inhibitor last put in? Had any aditions to the system recently? Also if there's a restriction somewhere it may pay to try the pump on a lower setting see if that reduces the 'noise'..