I built this house on a slab 5 yrs ago. Well water to a storage tank to a booster pump to a pressure tank to the house. (2 story) Plumbing was initially laid in slab for Hot H2O recirc. On finish out with hot H2O tank upstairs plumbers installed recirc line to TACO pump T'd into cold side of H2O tank inlet. A swing ball valve for shutoff is all that is visible out of wall for this cold supply. Water flows from this T to cartridge recirc pump into a separate system to recirc. To house

I got tired of pump running 24/7 as we are gone a lot so I put a timer on it. About 4 months later water hammering starts and stops when any faucet is turned off then on. Hammering seems to come from inside wall area where cold supply is but it could be transmitting from somewhere else. I opened hot H2O relief valve and drained some but hammering still there. Any suggestions?

You need to drain more of the system if you are trying to eliminate water hammer. Shut off your main, flush all toilets and open all faucets, open the stops below each sink and toilet and allow to drain. That should replenish any air chamber that may have filled with water.

OK I will try but when you say open the stops below each sink do you mean assure that the shutoff valves are open? I assume you mean I don't need to drain hot H2O tank. Small things like the fridge water line? The washer shutoff is in a tough area to reach. Thank you.

No on the hot water tank and yes on the shut off valves. They are actually called stops, disconnect the tubing that comes out of the stop and then open the stop.

Drained everything. I may have found culprit. The area where I had been hearing the hammering started again intermittently without the pump on. It all seems to be caused from the shower/body spray valve in the freestanding wall of the shower wall. I can make the pipe rattle by quickly turning the shower handle on/off. Weird.

Please, take photo of the heater/pump set up and its connections and post it.

OK. Give me a couple of days to get it posted. Thanks

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That brown fixture looks like a booster pump or recirc pump, what does the label say on the side?

That's the TACO recirc pump. It's a bronze model 007-BF5.

I replaced the cartridge in he recirc pump ($100) and it still hammers off and on sometimes with the faucet on sometimes with it off. Very intermittent. It is definitely coming from inside the wall immediately below where the recirc pump copper pipe feeds into the system not more than 2 feet linearly away. Only hammers when recirc pump is plugged in.