water hammer when water hot

[kprida]

Recently whenever our hot water is fully heated, that is the cold inlet is warm. We are getting water hammer for a few seconds. This only occurs when the tank is fully heated. Its an unvented system. The pressure relief valve has been changed and the expansion vessel recharged. The only thing not done was the strainer checked. Could this case water hammer?

I'm assuming that the water gets hot, expansion vessel takes the strain. Turning the tap on the expansion vessel and cold inlet fight?

Hope this makes sense.

 

[josh]

hmm is a bit of a tricky one, i would say check expansion vessel but you'v done that, the strainer wouldnt cause the knocking but the check valve could knock.
Does it do it when any hot tap is used or just one paticular one, could be a check valve in that, had that before. knocking/water hammer can be very deceiving.

 

[kprida]

hmm is a bit of a tricky one, i would say check expansion vessel but you'v done that, the strainer wouldnt cause the knocking but the check valve could knock.
Does it do it when any hot tap is used or just one paticular one, could be a check valve in that, had that before. knocking/water hammer can be very deceiving.

It happens with any hot tap, or the shower. Only get it when the cold feed has warmed up, making it awkward to track down.

Forgot to add if you open a hot tap slowly and drain some off before opening properly it doesn't appear to happen.

 

[tweakyboy]

Change the vessel, I've had the same problem before and changing the vessel fixed the problem.

 

[josh]

think then i'd be tempted to change the vessel to, would put a screw driver to the check valve just before the cylinder and make it do the noise to see though.

currently we'v got the same problem on a megaflow, recharge the air gap and fine for only 2 days then back again, i'd suggested fitting an external vessel but my dad (another plumber) went round there and says its the check valve on the kitchen sink tap yet when i went there first the man said it was everything in the house that made it do it yet when he went round said it was just the sink ? lol.

 

[kprida]

I believe it could be the vessel. I reduced the pressure to 2.5bar and now the sound is less aggressive and it seems to occur at the point the vessel is just about to empty itself. Its like a bouncing sound inside it. I guess it spluttering for some reason.

 

[Toxic Ted]

What size is the preasure vessel

 

[kprida]

It's a 12 litre (zilmet 110 ultra pro). Definately appears to occur at the point the vessel has just about emptied itself of water.