Only Bangs when thermostats satisfied.

qtown

I have a 20 year old Burnham Hot water Boiler that's worked perfectly. Converted gravity system, original piping and column radiators, with a Taco110 circulator. I have 2 HTX 60 expansion tanks installed. This is the 3rd straight heating season I've been putting up with this problem. The thermostat calls, pump goes on , house is heated, thermostat is satisfied, pump shuts off. Any where from 3-5 minutes after this sequence I get loud banging from the pipes inside the walls.

It is always the same banging, like someone is banging on them with a hammer. and it is not from the radiators. Boiler temperature usually stays at 140, Boiler pressure at 20psi when circulator is running, slightly less when it's not. Can't bleed any air out of the radiators. And it doesnt' matter if I turn the pump on for just a few minutes and turn it off before the boiler water gets a chance to heat up, so I don't think it's expansion. This problem is driving me crazy. Any ideas anyone?

RobbieDo

Need more info

What type of zone valves do you have, or is a pump running the zones? Why would you try and bleed air out of the radiators, there should be boiler drains where the boiler is. Are you pumping away from the expansion tanks? How many floorsmis the house?

qtown

qtown

No Zone valves, 1 zone with a 110 circ, on return. Been like this for 20 years with no problem until recently.

Tim McElwain

Is the banging

on the return piping side or the supply side? Or can you even tell. It sounds like water hammer due to some restriction in the system perhaps or piping which slowly expands due to heat on the run cycle but then when pipes cool down and the pipe contracts it falls back into its original position. You will have to track down the exact location and then perhaps open a wall to find the cause. Sorry but that is all I can see to do. I am assuming you do not have any flow checks on the system if you do that could be causing the problem. Have you checked the flow control valve to make sure it is working correctly? I again assume you may have one if in the past you got domestic hot water from the boiler.

RobbieDo

Bang

You said it doesn't matter if the boiler is cold, you start the pump then shut it off and the bang still happens? Is there flow controls in the line?

qtown

thanks for the input

No flow control valves, there is a separate hot water heater . Down by the boiler there seems to be more of a vibration on the supply piping than the return. If I could pinpoint the location I'd gladly open the wall. 

RobbieDo

Pump

Which side is the pump on, supply or return? Are you pumping through the boiler or out of the boiler? Are any of the valves partially open? Do you have pics of the system? That might help as we don't have much info to go on.

qtown

PUMP

Is on the return. There are ball valves before and after the pump, and they are both wide open 

RobbieDo

Pics

Well, with the lack of info and you said nothing has changed. It is going to be difficult for us to help with your issue. Your boiler temps of 140 are very low for a non-condensing boiler, there is an issue there too.

Big Ed_4

What Has Changed

What was changed on the system at the time the problem started ?

Gordy

Expansion tank pressure?

Are they set to the proper psi when isolated from the system?

qtown

HTX60

Heating contractor added an additional HTX 60 in line with the existing. I am told the boiler pressure on the gauge at 20psi is slightly higher than it should be.

Adding the Expansion tank did nothing to alleviate the problem.

qtown

expansion tank pressure

I'm afraid I don't understand how to answer that. 

Gordy

checking tank pressure

 There is a schrader valve on each tank check with a tire pressure gauge. The tank should be isolated from the system when doing so. It should check out between 12-15psi unless you have a really tall house of more than 3 stories.

qtown

been shoveling roofs

Priorities! Expansion tanks read just under 15psi