Clanking Boiler

[chadvandonkey]

Anyone have any ideas why my boiler has started making clanking and banging noises whilst its working? Is it a sign of near death?

I tried some boiler quietening liquid but it didnt make any difference.

It makes a right noise that seems to echo along the pipes

There is some air in the system that I can't get out - shouldn't the system vent itself into the loft tank???

It happens more when it's just the HW circuit thats running so I suspect too much air in the system but how do I get it out?

 

[Ronald0]

HW (primary) circuit should have cylinder heating coil upstand bleed on flow to cylinder.

Clanking/knocking/kettling is usually circulation fault. Check level of water in F&E tank, pump integrity/speed, air in system, blockage due to crud. Is noise caused by steam and water venting into F&E tank?
Has boiler lost its pump over-run facility?

 

[chadvandonkey]

I've recently flushed the system several times after fitting a couple of new radiators which is how the air has got into the system. And again the other night I drained the whole system off and it's no different after a week of normal running. The pump may be on it's way out but it seems to be working ok and doesn't make any noises or give any indication its failing.

The loft header tank is full and working fine - is this the F/E tank you mention? There shouldn't be any crud in the system as it's been flushed probably 5 times in the last 6 months and it always runs clear.

Doesn't the system vent itself into the loft? Could the vent be blocked?

I've not seen a bleed on the cylinder coil or in the airing cupboard anywhere - only a couple of stop valves. Can I bleed the system by loosening the big nut on the pump?

The noise comes from the bolier itself and then down the pipes. After the boiler has switched off it sometimes lets out a big bang/clunk like metal expanding / contracting.

Sounds like it's an airlock problem but I'm not sure how to get it out.

 

[Biguns]

Does it only happen after the boiler has switched itself off

 

[chadvandonkey]

No the noises and clanking are whilst its running and the odd bang after its turned off

 

[Biguns]

See FAQs 9 & 14 here

//www.diynot.com/forums/viewtopic.php?t=175736

and report back what you find. Also try increasing the pump speed

 

[Ronald0]

The pump may be on it's way out but it seems to be working ok and doesn't make any noises or give any indication its failing.

Doesn't the system vent itself into the loft? Could the vent be blocked?

I've not seen a bleed on the cylinder coil or in the airing cupboard anywhere - only a couple of stop valves. Can I bleed the system by loosening the big nut on the pump?

The noise comes from the bolier itself and then down the pipes. After the boiler has switched off it sometimes lets out a big bang/clunk like metal expanding / contracting.

Does the pump respond correctly when you change the speeds; does it vibrate, is it noisy?

Removing the large slotted screw in the centre of the pump will only bleed the pump as hardly any water will come out following any air.

The system does vent into the F&E tank in the loft. The vent pipe and the flow into the system from the F&E tank can be checked for blockage by first loosening, and putting a hose on. a downstairs drain valve and then taking your garden hose up to the loft and hosing them through. This is a good way of cleaning the system out. Set any motorised valve to manual.

Does your boiler require pump overrun? Is that facility still functioning?

 

[chadvandonkey]

At the expense of sounding thick how do I increase the pump speed? Is there a switch or pot inside the tbox? Could this have been affected by adding 2 extra double rads to the CH loop?

It seems fine when on CH mode there's little if any clanking but on HW it does it and I can hear the air bubbling and gurgling round the boiler loop. I thought it should vent itself over time and the bubbles find their way out.

Sorry I don't know what you mean by boiler overrun. Will check the sticky above to see if its mentioned on there.

 

[Ronald0]

Most domestic pumps have three speed rotating dial at the terminal end. Switch it round to max.

If you still suspect air in the hot water circuit and you have no upstand bleed valve, look for a drain valve on the boiler.

With the F&E tank ballcock still feeding in water and the motorised valve open on HW circuit connect a hose to the boiler drain valve and open it. Allow it to run water for a minute or two, look for air bubbles.

Still suspect air in circuit, then setup your garden hose to reverse flush into the boiler drain valve, water and hopefully any air will exit into F&E tank.

Pump over-run is a requirement for most boilers in order to carry away heat immediately the boiler has shut down due to latent heat of steam allowing the stationary water to boil in the heat exchanger. The pump, controlled by a pump delay thermostat, will therefore run for 5 minutes or so until the thermostat cools, thus switching off the pump.

If this facility has been lost due to thermostat failure, water and steam will exit the vent pipe with much clanking and banging.

 

[chadvandonkey]

I checked the pump speed and it's on the fastest of the 3 settings.

There is a drain valve on one of the pipes inside the boiler cover so I'll bleed some water out into the sink a little at a time and let it fill from the loft - hopefully that'll work. Should I buy and fit a bleed valve? Where abouts are they fitted? I'm guessing on the upper side of the tank coil feed?

Not sure about the overrun but I can check this tonight. Where do I find the pump delay stat? I guess it would explain the boiler letting out a big clunk as it's cooling down.

Thanks for the help

 

[Ronald0]

Don't drain water from boiler a little at a time; it needs a constant through put of water to pull the air through. Just make sure water is flowing into system at a greater rate than it is flowing out otherwise you will introduce air.

If you are handy you can fit bleed valve as you describe. Tee off heating coil flow with about 250 mm copper pipe pointing vertically and bleed valve on end. Ask at your local friendly plumbers merchants.

Pump delay thermostat is located on side of boiler heat exchanger inside case and wired to circuit board; check in boiler installation manual.

 

[chadvandonkey]

I've tee'd off the feed to the 3 way valve (in the airing cupboard) with a vertical pipe approx 10" long and put an isolation valve and an air bleed on the top as described. This hasn't been very successful as you can hear the air bubbles in the pipes but very little air actually rises up the vent pipe. Maybe I should have stuck with the 22mm pipe instead or reducing down to 15mm.

I've also bled the boiler using the drain valve inside the boiler cover and it's absolutely full of bubbles - literally non stop bubbles for an hour. The F&E tank in the loft kept the system topped up during the drain as per normal. I locked of the drain valve and within seconds you could hear loads of bubbles flushing round the system. There must be a leak somewhere that's letting in air as no matter how long you drain / bleed it it's still full of bubbles. I can only assume I've disturbed the pipework when I put the radiators in and now have a leak somewhere. There's no obvious leaks so I'll lift the floor boards to see if it's leaking under the floor where I fitted an extra downstairs radiator. I can hear a ticking of bubbles in the bathroom radiator which is where I tee'd off to put a new rad upstairs but I'd expect water to be visible on or around the kitchen ceiling if it was leaking upstairs.

As for the pump overun I'm not sure this is on my boiler as I couldn't see it in the manual - and it doesn't work if it should be on there either.

How do I do this reverse flush?

Thanks for your help so far.

 

[Agile]

Even if there was one then you should not be opening the combustion chamber to access it as ronald suggested.

I noticed you drained the system again to try to get rid of air. I dont understand why so many people do that but its the last thing to do, you want water and not air in your system. Have you bled the pmup?

Tony

 

[chadvandonkey]

I didn't drain the system I just let some of the water bleed out the drain valve (in the kitchen) with a hose into the sink whilst the F&E tank was putting fresh water in from the loft - trying to get rid of the bubbles and therefore clanking.

It's looking like the best way to fix it is with a new boiler full stop.

 

[Agile]

A new boiler is unlikely to fix any of your problems!

Tony