I have a propane boiler that blew the pressure relief valve. Output temp at the time was 154 df. Since then, there has been knocking sounds in the pipes. Someone raised the set temp to a 150 df. I normally set the temp at 130 df and seemed to work fine. What could be the cause of the sounds?

Hello ailfan

There are two main causes for knocking pipes : either water hammer or water rushing by something that is loose.

As you stated that there was recently a repair, air in the pipes is the most probable cause.
Find the boiler air release valve, and let the air escape. You may have to do that several times.

Success !

:)

i have a propane boiler that blew the pressure relief valve. output temp at the time was 154 df. since then, there has been knocking sounds in the pipes. someone raised the set temp to a 150 df. I normally set the temp at 130 df and seemed to work fine. what could be the cause of the sounds? 150 degrees is a high setting. The heater comes out of that factory set at 120 degrees.
Describe the knocking. Is it coming fron the heater or the pipes? Does it happen when the gas is on or does it happen when you close a faucet?
Do you hear the "knocking" even when no water is being used? Talk to me, Tom