Water hammer when boiler comes on.

[Rageyboy91]

Hey there,

I'm getting a large bang when the boiler comes on, I have a 25mm mains that runs to a stopcock then about 4m of 15mm piping to the boiler.

When my heating comes or using the hot water tap I get a water hammer bang? recently it's become super loud and it's starting to concern me, it sounds like it's under the floor.

Would a water arrester help, or is there a problem with the installation that needs sorting? It's a brand new 2021, viessman 100kw.

cheers any hell would be great.

all the best,

matt.

 

[Johntheo5]

A E.vessel is advisable and required by some boiler makers now, especially where DHW preheat is an option as the expnded water cannot expand back through the mains if a water meter or a PRV is installed, yours seems a different problem but installing a shock arrestor cannot but help IMO.

 

[Rageyboy91]

A E.vessel is advisable and required by some boiler makers now, especially where DHW preheat is an option as the expnded water cannot expand back through the mains if a water meter or a PRV is installed, yours seems a different problem but installing a shock arrestor cannot but help IMO.

Cheers, I did notice this online that boiler manufacturers seem to be recommending them when researching the issue.

It's only become a recent consistent problem. I'll email the boiler installer see if they can help.

Luckily the floor is all old and has already been cut to lift up.

Cheers.

 

[Madrab]

If the knock is when the heating comes on too then it's may not be anything to do with the mains water as they are separate systems, it could be a loose pipe knocking when the pump kicks in.

 

[Mister Banks]

I have a similar issue but the knocking only happens occasionally and only when the boiler pump turns off. I have spent many hours trying to stop it but have given up.

 

[Rageyboy91]

Luckily I had it installed with heatable so an engineer is comming to check it out. It's just been so loud recently just terrifying lol

 

[Rageyboy91]

Morning, this is fixed now it needed a new diverter I think. Was a 10 min job under warranty.

The part has a small plastic actuator that goes up and down. It looks like that was misbehaving when firing up. That's 2 parts in 2 years it's not boding well for the viessman 2021 30kw.