How to find source of water hammer

[James1979]

Hi - for some reason, we've started having loud water hammer when most of the outlets are turned off.

I've got quite good access to the pipes so can physically see it shake when something is turned off but I can't work out what's causing it as it seems to be nearly all of the outlets that cause it, not just one or two.

From the rising main, the water first goes to a bathroom (that does cause the water hammer), then it tees and one arm goes to a kitchen inc dishwasher and w/m (which does cause it), then a toilet and sink (which DON'T cause it). The other arm of the tee goes to the tank in loft which then feeds the cylinder, shower and header tank (which don't cause it).

There hasn't been any work that would change the system so I'm finding it really hard to work out what cause is. Have tried turning pressure down but no difference.

Any ideas on how to identify cause? Thanks in advance,

 

[John the plumber]

So am I right in saying everything downstairs causes it but everything upstairs doesn’t?

 

[Madrab]

You wouldn't be able to turn the pressure down unless you have an adjustable pressure reducing valve (PRV). You'll be turning the flow down at the stop tap I would guess.
Most instances of water hammer are created by higher water pressure and valves turning off too quickly (1/4 turn ceramic valves/solenoid valves on dishwashers washing machine/toilet valves etc) and badly fitted/loose pipework.

2 usual ways to fix:-

1) install a PRV & 2) Clip/Secure loose pipework

 

[James1979]

Thanks for the replies - no the bathroom is upstairs (with water hammer), kitchen downstairs (with) then back upstairs to the en-suite (without).

You're right - I don't have a PRV, I just reduced flow at the internal stopcock. It's all the valves in the rooms mentioned including normal taps in bathroom (sink and bath), toilet, tap in kitchen, D/W and W/M.

I suppose somewhere it might have come unclipped but I've been in the house for 5 years without an issue or change to the pipes which is why I'm puzzled where it's coming from. If it was dodgy pipework I thought it would have always been there. Maybe it's worth fitting a water hammer arrestor but wasn't sure where to fit it as there seems to be more than one place that causes it?

 

[Madrab]

Your water pressure may have increased due to the mains being altered. Invariably they upgrade/turn up the district service if there are new estates/industrial works etc being built, then it depends where you are on the service etc.

Best idea would be to check the mains pressure first, anything above 3 bar then I'd fit a PRV.

I'd only fit an arrester if all else fails, as they invariably require maintenance, never had the need though. They don't actually correct/remove the hydraulic shock, they just absorb it.

 

[James1979]

Thank you - that is a great suggestion I never thought of. There are 5 new houses that have just been built directly opposite our house and people have moved in about a week ago so that would make sense. I haven't got a pressure gauge but will pick one up from Screwfix and see what it says. I'm assuming by your post, if it's above 3 bar then fit a PRV and reduce to 3? Thanks again,

 

[Madrab]

Yes, that would be the ideal. If you still get hammer after that point then I'd advise looking at what's creating it rather than an arrestor to 'hide' it.

 

[James1979]

Great advice re pressure. Pressure gauge arrived today and shows between 6.5 and 7.5 Bar (changed a bit each time I tested but never below 6.5). So off to buy PRV tomorrow and hopefully that’ll fix it. Thanks again.

 

[Madrab]

Wow ... way high, yup, get a PRV on it to start with

 

[SpecialK]

I had water hammer that came from the rubber in the stop cock - I guess it wasn't attached properly. After screwing in the stop cock really tight, then undoing it again the water hammer stopped... I replace the rubber in the end.

 

[Alec_t]

Another possibility is the ball-cock on the tank not shutting off properly. A new washer can cure that.

 

[James1979]

Thanks for the other replies. I think the tank and ball-cock are ok as it’s shutting off fine and it doesn’t actually cause the hammer when the tank fills and stops. I’ll try to stop-cock though just in case - I’m guessing you mean to just close it tight then open it? Not tighten the gland nut? Thanks again

 

[SpecialK]

Yes just the handle in tight so it picks up the rubber properly again, or turn it off outside and replace the rubber?

Thanks for the other replies. I think the tank and ball-cock are ok as it’s shutting off fine and it doesn’t actually cause the hammer when the tank fills and stops. I’ll try to stop-cock though just in case - I’m guessing you mean to just close it tight then open it? Not tighten the gland nut? Thanks again

 

[James1979]

Thanks again - going to try PRV first today (and will have to close stopcock for that anyway so will try that at same time) and if that doesn’t work I’ll have to trace the pipe and clip any bit that looks a bit shaky and hopefully that’ll sort. Thanks.

 

[James1979]

PRV fitted in about 15 mins. Adjusted to 3.0 bar. Water hammer gone!

Thanks for your replies.