Water Hammer

radmix

I just read Dans artical on Water Hammer in steam systems. What would cause water hammer in a hydronic system. I have a customer with radiantors and an oil fired boiler. He says when the boiler fires for a while the radiators bang so loud he thinks the radiators will split. Two zones of heat with Circs on the return and a old tank type expansion tank off of the boiler top. The only thing I can think of is the circs are piped in the wrong location.

kcopp

That sounds more like expansion noises. A cold (65F) radiator w/ 190F water slamming into it is a quack period of time will certainly cause expansion. I am guessing that this is a tankless boiler...no indirect water heater and the boiler is hot 24/7.

icesailor

Something else is wrong. Like a failing High Limit, not enough pressure and water loosing pressure as it rises in the system.

It has nothing to do with the fact that it is a warm start or might have a Tankless Only and not an indirect.

If the High Limit is set to 200 degrees, and the limit is failing, you can have hot water well over 240 degrees which will boil as the internal pressure drops. This is not a common problem with the banging as described, or we would all know about it.

I've seen it with the Honeywell control with the long capillary tube, or the same control without the capillary tube but the control going bad.

If they are cast iron radiators, 170 degrees should be all you need. And a hot water storage tank.