Hi,
I have a wood combustion furnace system installed 6 year ago. Till now everything was silent and this year suddenly the water heating circuit began to click about every second when system switches to this circuit's pump. After the water is heated to preset value the pump is turned off and clicking noise disappears. The pump is about 30 foot distance to furnace and the noise is like coming from furnace. Pipes are outside tied on the walls and are from copper. The only thing I changed in the system is that I set furnace heating temperature 10 degrees higher which is still lower a little bit than recommended temperature. I was searching for answers on internet but found the frequently happening water hammer noise that is caused by suddenly closed valves, high velocity, or heating pipes etc. My problem is that this hammer noise is like I would stay with a little piece of wood in my hand and hit the pipe every second like an old clock. Firstly I thought pump is faulty, but it actually does not seems to be, as when I am listening very close only a very silent water flow is heard and clicking noise is transmitted through copper pipe I think. This is what I hear. If it helps, when I put my hand on the part of pipe where the noise seems to be the loudest I feel a mild hit.

It could be a faulty tempering (mixing) valve or a faulty check valve (or flo control)... check to see if either one of these in near the "clicking noise"... may have gunk built up on the inner parts.

Mark

Thanks Mark, I have some one-way valves and possible valve where the noise is coming from is on a pipe that is coming out directly from furnace than takes about 20 feet long and ramifies in 2 directions to hot water circuit and to warm up circuit, so this pipe is common for these circuits and noise appears only when hot water circuit is in use. Both pumps for circuits are on the other side of 20 feet long pipe. I don't really know what to do and I would like to locate well the faulty part because there is cold out there and cannot stop furnace for long time to empty the system.
Another thing I haven't mentioned is that this year I increased with 10 degrees the warming agent still below recommended, but used 2-3 years ago at this temperature.

It's possible that when you made the increase, the valve you touched (tempering valve?) became unseated. I'd check this first...

I think I am closer now. It is about recirculating area. There is a pump, a check valve and two taps after and before them. When recirculation pump is on, knocking stops suddenly, then when pump is off knocks again. I tried to locate sound on this 4 feet long recirculating circuit but not sure where is it coming from but close to the valve it seems to clang too a little when knocks. This area is easy to check as I can turn off taps and easily remove pump. Could it be this check valve faulty or built up dirt?

Some check valves come apart pretty easily... just unscrew and then unhinge the flapper to test. Reinstall the nut (without the flapper) and test the system. If sound is gone, replace the check valve...

Thanks for support, as you have helped me a lot. It was the spring inside check valve the faulty part. Now the rest of the job is to free air from the heating agent.

Awesome news! Thank you for the update!

Mark