0

I've been changing the thermostatic radiator valves on my radiators.

My understanding (obviously wrong) is that if the TRV 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 TRV you'll have to catch the entire contents of the radiator and then change the TRV.

In my house there is a pipe from the floor into the TRV, 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?

0

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.

  • So, if my boiler is showing pretty much zero pressure, yet I haven't drained the system so there is water in the pipes - if I turned the boiler off and removed the TRV from a radiator, would the pipe going into the TRV splash water everywhere, or remain level as no pressure is there to push it out? There are many contradictory answers online where people say yes, and others no! – Ricky Nov 13 '18 at 12:04
  • I can not answer your question with a definite answer since neither you nor I know if the gauge is reading correctly. theoretically, if the gauge is reading correctly their should be no water in the system but we know better. The pressure could be at zero and still have water in the system. If you were to open a valve at the boiler in a closed system such as yours the pressure will fall until it reads zero. The water would be held up by the negative pressure above the water level. What you could do would be to very carefully loosen a fitting at the radiator's bottom to see if water flows. – d.george Nov 13 '18 at 14:52
0

I can not answer your question with a definite answer since neither you nor I know if the gauge is reading correctly. Theoretically, if the gauge is reading correctly their should be no water in the system but we know better. The pressure could be at zero and still have water in the system. The zero reading could be generated by a vacuum above the water line sufficient to reduce the gauge reading to zero. If you open a vent at the top of the system and allow air in, the water will seek a level and again show a pressure on the gauge, equal to the height of the water above the gauge. The only thing you could do would to be to open a vent, allow the water to seek a level, then loosen a fitting at the item you want to replace and see if water comes out after the sucking sound goes away. If not, the water is probably below that point. This is the best explanation I can give. Remember , 1 foot of water = .433 pounds of pressure or 1 pound of pressure = 2.31 feet of water elevation. Hope this helps (sorry I answered twice; 1 answer and 1 comment

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.