Worcester Greenstar 28i junior - Possible Water Hammer?

[swa110w]

Whenever our combi-boiler (Worcester Greenstar 28i junior) turns OFF, it makes quite a noise. This is tolerable during the day but it is very disturbing at night when the boiler periodically comes on (presumably to keep things moving or pre-heat the water, not sure). It seems to echo along the pipes and where they enter the house (the boiler is in the garage) is right below our bed.

it's an abrupt shut-off noise, followed by a rapid series of tapping/clunking. It only lasts a few seconds but it is very annoying!

I'm guessing the noise is water hammer, though I'm no expert. I've stood next to the boiler when it turns off and the noise seems to be coming from the boiler itself (though again, I'm no expert).

Can anyone give me any ideas on what to try? Could it be the boiler itself or is it likely that I'm hearing an echo along the pipes?

 

[bazdaman]

What does the pressure gauge read?

 

[swa110w]

1.5 at the moment (right in the middle of the green), though I've let it drop to around 1 and it's made no difference.

 

[CombustionGuy]

Is this when you use Hotwater? If so check it does it from another tap if it doesn't it's your washer in your tap

If it does have you got a vessel on the cold water incoming? This can help this issue.

 

[swa110w]

It is when I use hot water but it doesn't happen when I turn a tap off, it happens when the boiler stops firing.

So if I ran one (any) of the hot taps, the boiler would come on. If I turned off the tap, the boiler would continue firing for another 30 seconds or so and then switch off making the knocking noise.

I don't know about a vessel on the cold water incoming. How could I tell?

I do know that the cold water taps seem to turn on and off with a lot of pressure - there's usually a thud when I turn them on or off. Could that be related?

 

[swa110w]

Where would a vessel or arrestor or whatever they are called be located in my system? The water comes into our house and into the garage where the boiler is.

 

[swa110w]

I've had a plumber come and look at the boiler. He didn't seem to have much of a clue either!

He didn't think the knocking noise was coming from the pipes, especially as they appear to be well-fastened throughout the house. He thought it was coming from the boiler itself and wondered whether it could be the fan as it slows down? The boiler is clearly working, as we have no problems with the hot water. Could the fan be the problem? Is this common?

He also noted that our water pressure is very high, which is probably causing the (unrelated) thud when the cold taps are turned off or the toilet stops filling. He said he could fit a pressure limiting valve but couldn't guarantee that would solve it. We can't turn our internal stopcock down a bit as we've got a SureStop switch. Could we turn the external stopcock down a bit?

P.S. I'll try and get a video of the boiler knocking noise later.

 

[swa110w]

As promised, here is the video of the noisy boiler. Anyone got any ideas?

As I mention in the YouTube description, ignore the noise at 0:13 - that's me tripping over a bucket. The noise I'm on about occurs at 0:38.

I should add, I realise it doesn't sound much but, as I mentioned earlier, it really echoes down the pipes, and is especially noticeable at night.

 

[swa110w]

Anyone?

 

[jeff the gasman]

From what I heard it sounded like overheating.
Possibly a circulation issue.
Get a decent boiler guy in .
Jeff

 

[swa110w]

Wouldn't that result in the boiler cutting out though? Bear in mind, this noise only occurs as the boiler is shutting down.

(he says, speaking from absolutely no experience whatsoever!)

 

[jeff the gasman]

It's possibly shutting down because it's overheating.

 

[swa110w]

No, it shuts down when I finish drawing the hot water.

So I'll run the hot tap, the boiler will kick in... I stop the hot tap, and maybe 30 seconds later the boiler shuts off too.

It isn't shutting off incorrectly.

 

[jeff the gasman]

You obviously want a definitive answer.
You don't give any thanks.
Get a decent boiler engineer in or put up with noise.
Jeff

 

[swa110w]

No need to be like that, Jeff.

I wasn't expecting a definitive answer. I was merely trying to solicit advice and, where possible, provide clarification.

I'm sorry I haven't laced my posts with the requisite amount of praise but, rest assured, I'm extremely grateful for all of the comments on this thread.