converted to Y-plan getting loud bang

[SkinnyOl]

Hi all,

I am wondering if anyone can give me some advice please.

We have replaced our boiler and at the same time converted from semi-gravity to fully pumped. The y-plan layout now includes a separate pump and a 3-port valve.

It all works, but there is a loud bang happening frequently which I can reproduce manually as follows:
The CH and HW are hot, everything good, the pump has switched off.
There is a little lever on the 3-port valve for manual switching. I pull the lever on the 3-port valve into the HW position. As the HW is hot enough, the lever immediately starts to move back to the CH position, slowly. As it is switching, this is exactly the point when the bang happens. The bang comes from the pipework further away in the house.

When I switch on the pump and do the same test again then there is no bang. The lever is also easy to pull while the pump is running.

The pump has settings 1, 2 and 3. Running it at 2 makes it bang louder than at 1, presumably increasing the pressure.

I'd be grateful if you could help.


Regards,
Ol

 

[RigidRaider]

Get the plumber back. The ball that moves on a short arm inside that Y plan valve to close the ports is worn or damaged and is shutting the ports abruptly causing water hammer.

I changed ours, which had started banging after about three years and now we have blissful peace.

 

[D_Hailsham]

There is a little lever on the 3-port valve for manual switching. I pull the lever on the 3-port valve into the HW position. As the HW is hot enough, the lever immediately starts to move back to the CH position, slowly.

The lever is not for manual switching; it's there so the valve can be set to mid-position when the system is being filled/emptied.

You can't "pull" the valve to the HW position, it is spring-loaded to go there automatically.

Check that the valve is the correct way round! The three connections are marked A, B and A/B. A should go to the radiators; B to the HW cylinder and A/B to the pump.