Hammering sound in hot water heating system

dbessey

System has recently developed a “hammering sound” during heat up. Not your regular creaks and clicks of expanding pipes, but rather a “hammering on the pipes rapidly with a rubber mallet” sound. System is running between 20 and 25 psi...typically between 100F and 140F respectively. Does not hammer everytime it heats up.

Older burnham gas fired boiler with cast iron radiators

Have checked each rad for air (manual bleed valves) Have not found any air trapped in any of them


What could be causing this?

Thanks

Darren

JUGHNE

Perhaps air in the boiler.....if you open the pressure relief valve you should get only water..no air.

nicholas bonham-carter

I hope the temperature does not get as low as 100 degrees f-130 should be the minimum to avoid an early rust out.
The pressure could be too high as well unless you have 4 floors.
Have you consulted a local hydronic pro, and what did he say?—NBC

JohnNY

dbessey said:

System is running between 20 and 25 psi...typically between 100F and 140F respectively.

So, you're saying the system runs at 20 PSI when at 100° and rises to 25 PSI when it reaches 140°?
First of all, you've got an issue with your expansion tank.

dbessey

Maybe I am expressing it incorrectly. When the boiler shuts off and thehouse is no longer calling for heat, i can watch the pressure guage drop to 20 psi and the temperature in the boiler will drop to 100F. It’s mild outside right now, so the boiler is not coming on very often (compared to the dead of winter when the rads are almost always hot)

Then , when the boiler kicks in (in the early evening, when the temperature outside drops off) the boiler sits around 25 psi and 140 F (actively warming the house and pump is on). Earlier in the fall we had a cold snap in november and the temp outside was -12 celsius. The boiler would ramp up and hit 30 psi and the relief valve was dripping. I think the compression tank was waterlogged. I emptied (reset the air cushion) the compression tank and the system now goes up to 25 psi instead of 30 psi when it’s hot (140 F). Valve still leaks some. I was told that might be normal. I think I will replace the relief next spring.

The house is a three storey home. Boiler in the basement..rads in the thrid level are not active disconnected the pipes up there years ago, bit the piping goes all the way up there so the head on the system is fairly high I guess......ceilings are 11 or 12 feet on each level of the home.

If there is air in the boiler, should i activate the relief valve to let it out? (Cool the system down first?)

Thanks for the feedback everyone, I appreciate it.

Small town here, no “boiler experts” around for quite some distance. The local guy is young and specializes in forced air and pet under the floor systems....just scratches his head when I talk about the boiler and cast iron rads........

Darren

nicholas bonham-carter

Probably the auto-fill valve is set for too high a pressure.
There should be some of the hydronic books from the shop here under your tree this Christmas!—NBC

dbessey

Hi NBC

Is it also possible that it is leaking by? I was thinking about your answer and thought that maybe i should let some water out of the system (boiler off and system “cold”..town water addition shut off) .....say drop the pressure in the system to 13 psi ...then close the system drain and open the system back to the town water. After the system stabilizes at a pressure...record that pressure ( should be 15 psi, i think)


Run the system for a week and then let it cool down again to the same temp (cold) and see if the pressure returns to 15 psi again. If ithe pressure is higher, then the pressure reducing valve is letting water in.........

Right?

Darren

EBEBRATT-Ed

I would suspect the expansion tank could be your problem