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Still have hammer, out of ideas...
I have two bedrooms over the garage. Both had water hammer. I fixed one of them today by raising the radiator about an inch. It's perfect now (other than the vent is a little noisy).
The second bedroom has an attached bathroom, both of which have radiators. This bedroom & bathroom is serviced by the same vertical riser (but a different one than the bedroom mentioned above). The water hammer remains, and it is at the start of the cycle. The hammer seems to occur in the supply line between the two radiators, however I'm not 100% positive.
I have raised both radiators as much as possible. I replaced a trap on one of them (the one in the bathroom - green walls in the picture below). The trap in the yellow bedroom appears to be functional based on the temperature measured by my infrared thermometer.
After about 20 hammers, the system is quiet and runs fine the rest of the cycle.
The vertical riser servicing both radiators is closer to the bathroom (green walls).
I know water hammer usually happens at the beginning of the cycle due to improper pitch, however since I raised the radiators as much as possible - this theoretically should have fixed it - no?
Any ideas would be greatly appreciated.