We've got an unvented HW system (hot water cylinder, oil boiler). There is an expansion tank fitted next to the HW cylinder.
The water pressure here is really high (has popped a few hosepipe fittings off etc) and the main stopcock is only open about halfway or so. When you turn on the hot water the flexi hose off the top of the expansion tank is banging away and causing pretty bad water hammer (but gradually settles). You can turn the tap on really slowly to avoid it but it's a pain.
I thought the point of the expansion tank was to prevent water hammer? I've also read something about replacing the flexi hose with copper pipe might help. Any thoughts on this before I dive in and make an arse of it?!
That big long floppy flexi hose looks to be the culprit. Worth replacing it with copper?
Could the flexi pipe not be secured to the timber above in some way to stop it 'flapping' around?
It appears to be long enough
It's an unvented system so be careful and seek proper advice before major tinkering
The mains stop tap at half open only reduces pressure when there is a significant flow, the static pressure will be unreduced.
My view is the water hammer is moving the Flexi pipe, not the Flexi pipe causing the water hammer.
@Bear is a plumber as are others on here
That flexi is not ideal. A copper run would be best. But mostly because flexis have a limited lifespan. 10 years would be really good going. Shorter is not unheard of. The rubber liner start collapsing and doing weird things. If it worked previously then replacing with new flexi could remedy it for another few years. But it might be something else.
As above, half cock doesn’t reduce static pressure. A Pressure Reducing Valve, if fitted, will do this job. Looks a bit like a PRV behind the flexi connector? As an invented system you really should:
1) not touch it DIY
2) have it annually serviced by a correctly qualified and registered plumber.
Getting a plumber out now to service would seem the only sensible move. They will check the PRV (if fitted) is set correctly and working, they will check the expansion vessel pressure, they may replace the flexi. If that doesn’t resolve the hammer, they may investigate further.
@big_n_daft - Thanks. I was just mulling this over and was about to type the same thing. The flappy hose is a symptom not a cause.
There's also some other botched stuff in there - two cold pipes secured using a metal strap, which in combination with the water hammer is going to wear them through pretty quickly.
probably time for a proper plumber I guess!
@goldfish24 - noted! We've just moved in so no idea history. There is a PRV above so time for a plumber.
What registration and quals am I looking for from a plumber for this?
We have a similar problem and so far a plumber hasn’t resolved having replaced expansion vessel and various valves
Ours is a flexi hose connecting the expansion vessel to the hot water tank. Maybe that does have something to do with it. Again no idea how long the setup has been there
Our plumber is qualified but he appears to be stumped
Again I would say the flexi hose is not the issue (currently have a similar problem on a recent install we did). We changed to copper pipe it and it has made no difference so am going to fit a small expansion vessel or maybe a PRV adjacent to the stop cock.
Don't think excess water pressure is my issue though as it is on the 6th floor of a converted mill!
I thought you could get water hammer suppressers, a T piece with a spring loaded plate in them which absorbed the sudden pressure rise when things like washing machine solenoids suddenly shut off etc.
Yes you can or a little expansion vessel, old school way was just a vertical pipe that trapped the air.
Two different issues surely?
Water hammer it what you get when there's air in the system and the whole thing starts banging as slugs of water have to accelerate past the air pockets, as a pipe 3/4 full of air means the water has to travel 4x the speed for the same flowrate. It them hammers into the next fitting and loses velocity.
Surge is what you get when you open a tap on the end of a long pipe, it takes a moment for that pipe to get upto speed, then when you close it there's another big bang as the water in the pipe suddenly comes to a stop.
To avoid water hammer you need to bleed the system.
To avoid surge you'd fit a PRV at the inlet to the pipe, and a pulsation damper/expansion tank at the tap end.
Don't think there is an official definition of water hammer but it usually means noise coming from some pipework!
A ball valve bouncing on the surface was a common cause of it.
What registration and quals am I looking for from a plumber for this?
I couldn’t think of the name when I wrote my post, just came to me - G3
“The G3 qualification, also known as an Unvented Hot Water qualification“