Noise Driving Us Mad

[vbasrar]

I hope that there is someone out there who may be able to help. We had a new combi boiler fitted about 18 months ago. Ariston Micro Genus II 31 MFFI. It was all working extremely well until a couple of months ago. Now whenever the heating is on we get this incredible noise from the pipes/rads. It is best described as a rushing sound and is noisiest from the pipes nearest the boiler. I have bled the radiators every day for since it started and still air comes out. Obviously it is a pressurised system but we don't seem to be loosing any pressure from the boiler. Nothing I do seems to make any difference and its driving me mad. Please help, I can't take much more of this.

 

[JohnD]

I suspect the gas you're getting is a result of corrosion, I don't know if you can put inhibitor in as it's a Combi.

Pumps can sometimes suck air in if their suction side is near an expansion pipe, but surely you haven't got one?

Does it help if you turn the pump speed down?

 

[andsam]

Your system was probably not flushed correctly after installation and is producing hyrogen. If the system is drained fully and refilled with some inhibiter it could cure the problem.

 

[chrishutt]

Forget hydrogen, it would never generate in the sort of volume you're describing. You've got air in the system, probably sucked in somewhere on the suction side of the pump.

Check for any sign of leakage below pump when pump is not running. Also check that system pressure is maintained at a high level (e.g. 1.5 bar) as this pressure will tend to overcome negative pressure around the pump inlet.

What is height of top of system above boiler? If more than say 7 metres you would need to set system pressure higher than normal level of 1.0 bar to avoid sub-atmospheric pressures at top of system.

Problem may be related to some other fault (e.g. sludged up DHW heat exchanger) which is increasing resistance to flow around circuits, thus increasing negative pressure zone on suction side of pump.

Does it help if you turn the pump speed down?

On no account turn down pump speed on a combi boiler! JohnD and others, please do not be tempted to give advice if you don't fully understand the issue. The questioner has no way of knowing that you aren't an expert.

 

[vbasrar]

Thanks for your replies so far. The noise does not happen when running the DHW side. A plumber friend has suggested putting some Sentinel X100 Gel into the system to reduce any possible air/hydrogen.

I could not turn down the speed of the pump as it has no speed adjuster anyway. I cannot see any signs of leaks anywhere near the pump/boiler at all.

When the system was last drained(which was after the noise started) it was flushed through for a week with one of the sludge removing chemicals. However the guy doing the work never put any sort of inhibitor in the system either when installing the boiler in the first place or after re-flushing it.

The boiler is installed in the upstairs back bedroom and is probably the highest point in the system. Would this make a difference?

 

[Agile]

Right now we have some info.

The boiler is near the top of the system which rules out most problems.

The installer is a dogey character who did not treat the water at all and had to come back to try to clean it afterwards. He is so dogey that he does not add inhibitor.

Drain the system and refill, adding a can of sentinel X100. Do NOT use cheap products! It may solve the problem.

Tony

 

[andsam]

I have come across many a new heating system that fills with massive amounts of hydrogen when the water has not been treated properly. I also think if there was a leak on the negative side of the pump you would get pressure loss when the boiler is at stand by. I would suggest you get the system treated properly by some one who knows what they are doing.

 

[vbasrar]

system has now been treated with X100. No difference so far but I know it can take a while.

It has also been suggested to me that it could be related to the microbore that is used extensively in the system. Possibly the sound is coming from a joint where the size steps down an creates a venturi effect. Is this possible or likely?

 

[ricarbo]

If the Sentinel was going to make a difference, it would do so straight away. It's a corrosion inhibitor, that's all. It stops the 'gassing up' in the future. It doesn't remove existing gas or air. I think you need to start again. Is the water black? If so, drain the system, refill with cleaner, following instructions. Then refill with inhibitor. A clean system has water in it that is straw colour.

 

[chrishutt]

It has also been suggested to me that it could be related to the microbore that is used extensively in the system. Possibly the sound is coming from a joint where the size steps down an creates a venturi effect. Is this possible or likely?

No.

 

[ollski]

Are you topping up the pressure as you bleed the rads?, just sounds like the pressure is low, are you reading the correct needle on the guage?. Sorry if its basic but needs clarifying.