One loud bang as the heating comes on

[Rodolphe]

It's been getting slightly worse with time. As the heating comes on, there's one bang in the pipes and that's it.

I haven't been able to isolate where exactly the sound comes from. Frankly Central Heating isn't exactly my strong point.

What could cause it? I am thinking that perhaps all I need is a small expansion vessel just after the circulator but it will seem to be like treating the symptom, not the cause.

As always, your ideas would be most welcome.

 

[dave1]

If it's doing it as the boiler fires up, I'd recommend getting someone in who's gas safe and can diagnose your fault.

 

[Rodolphe]

right, but the sound does not come from the boiler, plus it doesn't happen when the hot water comes on, so i am confident it is a piping pb, not a gas pb.

I thought perhaps something with the ch pump but..

 

[plum ber]

It could be as simple as fitting pipe clip's on the lofts pipes

 

[Rodolphe]

Thanks. I will trace the pipework and start with that.

I really need to work on CH. I've no confidence with it at all for some reason...

 

[Deleted member 25704]

It may be the capacitor in the pump. This device stores an electric charge which is needed to get the pump going on the start up. Overnight, this device may lose its charge, and hence a 'clunk' on the start up.

During the timed operation of the heating the capicitor is continually being charged so it is unlikely to make the same noise during constant operation.

If you have gravity hot water, and the pump does not cut in for this, then this explains/confirms the problem is indeed the capacitor.

Replace pump.

 

[dave1]

Could it be the 3 port moving over causing the noise?

 

[Rodolphe]

It could. I will check and report back on all of the above.

 

[Leo21]

Could do with a bit more info on the system. Gravity, fully pumped, make and model of boiler.

 

[wheeto]

It may be the capacitor in the pump. This device stores an electric charge which is needed to get the pump going on the start up. Overnight, this device may lose its charge, and hence a 'clunk' on the start up.

Sorry, what? I don't know anything about single phase AC motors, how is a capacitor needed to get a motor running?

Edit: OK I've found an explanation that makes sense, but it doesn't rely on the cap holding charge while the motor is de-energized.

 

[hammers4spanner]

blockage

 

[Billy Bob Bob]

bet its a trv

 

[Rodolphe]

All my rads work though.

 

[Mike Jackson]

I've had it with Honeywell 3 port valves as the valve moved over from hot water to heating. It was when the boiler had already been running and pump over run kept the pump running as the valve moved over. The hot water circuit shut with a bang. I solved it by putting an auto bypass in.

 

[Rodolphe]

I am going to take back some of what I wrote: there is also a problem when the boiler ignites.

Is there a GSR around Croydon willing to look at it in the coming days?