Water hammer with hot water?!

[torN]

Hey everyone,

I have an odd issue, when the water heater is on and I run any one of the hot water taps, I get a water hammer (trapped air) in the pipes next to the water tank. It does go after 10 or 20 seconds, I just think it is really strange, I know it can happen with cold water.

If the water heater is off and I run the hot tap this issue does not occur!

 

[Mel_P]

What sort of water heater - instantaneous? Immersion? ...

 

[PlacidCasual]

Water hammer is not air in the pipes. It is force transmitted to the pipe system as a consequence of rapidly closing a valve or tap and the momentum of the water is transmitted to the pipe work making a bang sound. It is normally a consequence of long straight pipe work runs and fast closing valves.

Are you sure you have water hammer? What does the effect sound like?

 

[Lokwyr]

If no air in the pipes, how is hammer eliminated by bleeding the system? Bleeding worked for me the last time I got hammering. Entrapped/ entrained air acts as a gas spring/ recuperator/ volume compensator and initiates pressure fluctuations resulting in harmonic resonance. Ok, the noise goes after a while, probably due to fluid hysteresis.
Of course- I could be entirely wrong with the theory but- bleeding and avoiding blind upward curves in the pipe runs works.

 

[PlacidCasual]

Trapped air would mitigate water hammer, it is the incompressability of water that causes the hammer. What does the phenomenon sound like?

 

[Lokwyr]

The (almost) incompressibility of liquids transmits the forces acting upon them. That's why vehicle brakes work. Apply a force at one end and the effect is felt at the other end of the fluid column. Trapped gasses get compressed and push back. The judder can be stopped by removing the compressible medium or in the short term by relieving the liquid pressure.

 

[Participant]

Hey everyone,

I have an odd issue, when the water heater is on and I run any one of the hot water taps, I get a water hammer (trapped air) in the pipes next to the water tank. It does go after 10 or 20 seconds, I just think it is really strange, I know it can happen with cold water.

If the water heater is off and I run the hot tap this issue does not occur!

Pic of the heater and surrounding pipework would be useful.

Also how long has this been happening and did it start after any recent plumbing changes?

Normally there's a check valve off the hot water...this might be faulty (or non existent).

 

[poosemon]

I had what sounded like water hammer recently. Took me a fair while to find what was causing it as was convinced it was my shower mixer tap (out of production so was worried i was going to need a whole new unit as no replacement cartridges).

After a couple of weeks, suddenly my kitchen taps started to drip a lot when they were turned off, turned off the water supply to kitchen taps and issue resolved immediately. Replaced the mixer cartridges for Hot and Cold on the kitchen mixer tap and havent had an issue since - £12 spent and a pretty easy DIY

 

[Kimi]

Had this recently when changing the mains pipe which goes from the stop **** to my balancing valve upstairs. Some how loads of crap got shot through and caught in the filter. Didn't know that valve had a filter but long story short after clearing it out the problem solved instantly

 

[ash_scotland88]

I'm desperate to solve mine, but I think it's long unsupported runs of pipes.

Toilet finishes filling up soft bang, washing machine or dishwasher water loud bang. Can control the noise with slowly turning off taps. But to secure anything down its carpets and floorboards up first floor and in the crawl space below the ground floor.

 

[DampDog]

I've not used them myself, but my mate installed a couple of water hammer arrestors. One by his WC is the worst offender and another by his washing machine. He recons it worked a treat for him. You can get them from Screwfix or a decent plumbers merchant. I am considering doing it myself. Our water pressure is pretty high so we get it. It tends to be one big "thud" when the WC finishes filling. If you have a tap even trickling we don't get it at all.

 

[adamau5]

I thought I had a hammer. Turned out it was a bad tap washer in the utility room. Took a year to chase it down! Just by chance whilst the wife was running the little one a bath, I was in the utility room. I knocked that Tap open and the noise went. Replaced internal gubbins and now silent.