Boiler knocking and banging

[TR1CKY]

Maybe a coincidence but I replaced a radiator on Monday night and tbh, we didn't notice anything (but it may have been quietly rumbling) but now upon start up, the boiler crashes and bangs.

I've bled the system and no rads have any air.

Pressure is at the recommended 1.5bar.

Upon visual inspection, there are two (I believe) relief valves?

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• TR1CKY
• 19 Mar 2015
• 1

The right one is wet.

It's a Glow.worm 30HXi if that helps?

I have got a sludge catcher that was cleaned out about 8 months ago

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• TR1CKY
• 19 Mar 2015
• 1

Any idea what could be causing this banging. It doesn't sound healthy! Once the system is up to temp, it stops then it will go again, presumably on startup when getting the temp back up?

Cheers!

 

[45yearsagasman]

The top two are auto air vents and they may not be working. That Magna Clean looks like an accident waiting to happen.
If the two little black caps on the top of the vents aren't loose, then they won't work.
All I can say is ensure all air is vented from system and make sure you do something about the cleaner.
It certainly sounds like a circulation problem, but only a site visit will determine the exact cause.

 

[TR1CKY]

Thanks Pete. No air in any rads when bleeding and both the vents have loose caps.

Is there another way to vent the system?

 

[45yearsagasman]

There's a bleed screw on the Magna. Other than what you've done, there's no other way to vent a sealed system other than that. Best advice is to get the system checked over.

 

[TR1CKY]

Cheers Pete,

Bled and re-bled and there has been no banging so it looks like it was an airlock Yay!

I'll get the MagnaClean cleared out over the weekend Boo!

 

[TR1CKY]

I've got a similar issue to March time whereby the boiler is really banging and knocking, but only when it seems to have reached optimum temperature, i.e. just before it's about to turn itself off after getting nice and hot.

The relief valve (the one on the right) is spitting and gurgling when the banging occurs. Just seems to be heating only - when I ran the hot water for an hour, nothing.

Can't seem to upload video but it's here - https://vid.me/Vrsq

I've drained the system. I've bled from the bottom up and bled and re-bled both when cold then hot. Set the pressure to 1.3bar. Cleaned the Magna Clean. All the rads are letting water out when the bled screw is opened but the boiler still bangs. Bled from the Magna Clean too.

One downstairs rad isn't heating up - but it's one that has it's own drain off (which I used earlier). Not sure but it just doesn't seem "connected" to the system (I know it is though as it previously worked). Weird.

Any ideas anyone?! It's cold here...the mrs doesn't want the heating on until it's "safe"

Thanks in advance.

 

[Agile]

If the whole system is drained then that will include the pump.

If the pump has been drained then that needs to have air removed from it or it will not pump properly.

There are many different types but many have a large silver screw which needs to be loosened while holding an old cloth underneath to soak up a little water which will come out.

If that is not done then the pump can potentially be damaged but would usually survive and probably clear the air on its own after a few hours.

Tony

 

[Agile]

You have already been told that they are two "auto air vents" and not "relief valves" as you continue to call them!

 

[keego]

Have you got 2 zone valves near your pump (S plan)? If it's banging when it's reached temp it sounds like the bypass valve could be shut or maybe the rad that's not working now was acting as a bypass. Did that rad come on when it was on just hot water?

 

[TR1CKY]

Thanks for the replies.

After letting it settle last night, and re-bleeding, and setting everything a little bit lower temperature wise, the pipes are no longer banging.

However, the rad that not working is still on strike though. Not sure if comes on when just the HW is on, will have to test that later as that only comes on twice a day for an hour each time - 5am (wasn't up then!) and 5pm (but the heating is on from 3.30pm).

I'll keep an eye on my auto air vents