I've been changing the thermostatic radiator valves on my radiators.
My understanding (obviously wrong) is that if the PRV is turned off and the lock shield is off, that at that stage no water is getting put through the radiator, so by taking off the PRV you'll have to catch the entire contents of the radiator and then change the PRV.
In my house there is a pipe from the floor into the PRV , and then the TRV goes into the radiator. Is this the reason why it needs draining first – because the pipe from the floor will still pump water?
I had a leak earlier at the tail and was able to isolate at both ends, bleed the radiator (then tighten back up) and unscrew the tail. It obviously leaked while I applied PTFE tape but in this instance I didn't need to drain the radiator. It did, however, continue to leak more than I was expecting (one radiators worth).
Could someone clear this up for me please?
Best Answer
A hot water heating system has to have enough water pressure in the heating system (boiler, piping, and radiation) to keep the water up to the highest point in the system. So, for each pound of water pressure in the system, the water will rise up in the piping a height of 28" or 2.31feet. For example, if the height of the highest point in the heating system from an accurate pressure gauge on the boiler was 20 feet, the boiler static pressure or cold fill would have to be 8.66# (20 divided by 2.31). Most PRV settings are 12psi for a 1 story house and 15 psi for a 2 story house. So, if you remove the TRV there is pressure in the system that is being supplied by a PRV set at at least 12 psi If you want to remove any of the isolation valves you should reduce the pressure to a point that the water will not flow out of that pipe. MYself, I would drain the system. Hope this answers your question.