What would cause hot water pipes to make continuous thumping sound only at night?
Since we've lived in our house for a year we hear thumping sounds in the PVC pipes in the concrete slab foundation. If I turn the hot water heater off for a day there is almost no thumping sound. If I raise the water heater temperature for a day the sound is louder and faster that night.
I tried to flush as much sediment out of the water heater. It initially would not drain when I opened the water heater valve. Strange thing is that it only thumps at night.
System has no expansion tank or water hammer arrestors.
Re: What would cause hot water pipes to make continuous thumping sound only at night?
The fact that no water came out from the water heater drain when you turned it on indicates that you have a lot of sediments at the bottom of your tank. It's too late to try to clean your water heater now. You are looking at replacement, especially if your WH is older than its original warranty (generally 6 years).