water hammer on new gas boiler

alex375

We recently switched from oil to gas and had an IBC DC 20-125 boiler installed. Within days from the initial installation we noticed a loud banging sound when the heat is coming on. The contractor who installed the system came in and identified it as a water hammer and reduced the pressure in the system. For a day or two this appeared to have fixed it but since then the problem reoccurred. The plumber who installed the system is very responsive and has been in multiple times but hasn’t so far been able to pinpoint what the problem is. I was hoping that some of you could have a look at the set up (see pictures) and check if you notice any issues with it.

Thank you for your help.
Alex

JStar

The circulator needs to be on the supply, after the air separator. Check the install manual.

Is the circulator controlled by the boiler, or enabled by the zone valves?

alex375

Thank you!! It looks like you are right that the circulator is on the returning side while the manual does suggest it should be on the supply side. I dont know how to tell how the circulator is controlled.

JStar

It depends how it's wired, but we can maybe find out another way. Does the circulator ever run when the zone valves are all closed?

EBEBRATT-Ed

The circulator should be on the supply but that won't stop the banging. I would suspect a zone valve--fighting a check valve in the pump or a wiring issue. If there are check valves in the pump I would remove them. I see no need for them with zone valves

clammy

Aside from what others have stated ,when does the banging occur at beginning or end of a call for heat ,I think your installer should have added a pressure differential valve between your supply and return piping to prevent your zone pump from dead heading . Personally on my own jobs using zone valves I use a taco zone valve controller and wire my pump off of it ,this way the pump shuts off before the zone valve closes preventing dead heading or use the central heating pump relay in the boiler and install a by pass . I highly doubt boiler water pressure was the issue . I would also make sure the flow is in the right direction I also doubt the location of water feed and spriovent location is that critical weather on return or supply side of your primary secondary for your boiler .your zone valves are on the return side of your system correct ? Peace and good luck clammy

clammy

A closer look and it may appear that the end switches on the zone valves are jumped ? They should be tied into that taco pump relay not jumped if I see correctly peace and good luck clammy

alex375

Thanks for all the suggestions.
To answer some of the questions (as far as I can tell with my limited knowledge):
The circulator is controlled by the zone valves.
The zone valves are on the return side.
The bang occurs at the beginning of the call for heat when the circulator kicks in. The strength of the bang varies widely from barely perceptible to "the house is shaking". It also doesn't always happen, which makes reproducing it for the installer difficult. We were lucky it happened naturally when he came back the first time.