Loud regular knocking noise from a Potterton Suprima 80

[maxfox44]

Hello Everyone

I replaced the PCB about a year ago thanks to advice from this forum. The heating has been working perfectly ever since. Just recently the boiler has been making a very regular and loud knocking noise. It does this whether the water, water & heating or just heating is on. I think it might be a bearing on the fan or maybe the rubbers have gone. Before I have a look, can anyone suggest anything else?

Cheers

 

[Gasman28]

The fan sounds like the likely cause.
Do you have a pressurised system, if so, is the pressure low?
Bad system water circulation could cause boilers noises - either faulty pump or lack of water.

 

[maxfox44]

No, it's not pressurised. I also changed the circulation pump a couple of years ago after a Fernox clean and protect session. I did wonder about an airlock.

 

[Gasman28]

You must have a F & E tank in the loft, or somewhere high up. Check to see if you have water in this. Are you able to check if the pump is actually rotating? With the system turned off, undo the air vent screw ( large chrome screw on front of pump ) or Black plastic nut on Mysons to check the shaft. You should get a few drops of water coming out of the vent - normal.
//www.diynot.com/forums/viewtopic.php?p=266671#266671

 

[maxfox44]

Yes, there's a tank in the loft and the water level looks normal, more or less where's it's always been looking at the water stain.

I will check the pump tonight. The main reason for the inital question was that I think the noise comes on a little while after the fan is running. Which led me to believe it wasn't the fan.

 

[gasmick2]

it sounds like the system needs flushing out as sludge in the system will cause the heat exchanger to make knocking noises
just wondering when fernox was last replaced it only lasts about 5 years at the most, so it might be worthwhile replacing it its easier now as you can use the concentrate, drain some water from a radiator then with the help of a cartridge gun pump it in the rad and let it go around the system

 

[maxfox44]

I think you might be right. Last night I slowed the circulation pump down to no.1 and the knocking noise became very faint and stopped a for a while. I haven't had time to bleed the pump yet, but I will today. The Fernox was replaced two winters ago, after using the cleaner overnight.