Furnace leaking from PRV after appling pressurized water - Page 1
Forum section: electronics / general

author: MathWizard
author_rank: Super Contributor
timestamp: November 15, 2020, 04:28:56 pm
content: I have a furnace that heats water for baseboard rads, and tapwater. I was trying to get air out of the 2nd floor water loop, and at 1st I didn't remember what way the bypass brass-ball valve should be, and so I ended up appyling city pressure water to the radiator's waterbox, until the PRV opened. For now the 2nd floor loop seems to be fine again, the expansion tank is near empty of water, but the PRV is still leaking at a fast drip-drip-drip.The water temp and pressure gauge on the furance read normal, 80C and 11-12PSI, for a loop that about 20ft up from the furnace, 11PSI/2.3=25ft, so I guess that's about right.I hope I haven't screwed up anything, but that PRV never leaked before and it's being leaking for a few hours now. A while ago I opened it up for a few seconds, but not all the way. I shouldn't be messing with this without know more fluild dynamics.

author: Ian.M
author_rank: Super Contributor
timestamp: November 15, 2020, 04:46:10 pm
content: There's probably scale on the valve seat that's stopping it resealing properly. Using a heating system descaler*then flushing thoroughly at high pressure to get flow through the pressure relief valve *may* resolve it, but if not, the valve will need cleaning or replacement. As its a bad time of year to be without heat, I'd either replace the valve and attempt to refurb the old one as a spare, or buy one, to hold as a spare (or return for credit if you are skint), if the old one can be cleaned well enough to put back into service.* See if your furnace manufacturer recommends a particular product. Follow the product instructions to the letter. You may also have to check and possibly replace any anodes after using a descaler.

author: MathWizard
author_rank: Super Contributor
timestamp: November 15, 2020, 05:09:14 pm
content: Well I checked it again and it was more a tricle, then fast drips. So I opened it fully for a few seconds, and tapped it a few times when it closed, and for now it's dripping pretty slow, hopefully it will stop.IDK how old it is, but I do remember watching something that tis is how they fail, they get barely used, and then get used, then just break somehow.If I was do sit down for a whole day, just with calculus and some physics, and the EE analogies, I'd probably derive most the basics of fluid dynamics. I remember that dV/dt=A.v. Which won't apply much for my pipes though, since they are all about the same size everywhere, there's no standind rads, just baseboard pipes.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 15, 2020, 05:40:31 pm
content: Just replace the relief valve. They often leak when the seal has degraded from age, especially if tested.

author: floobydust
author_rank: Super Contributor
timestamp: November 15, 2020, 07:34:14 pm
content: What I do is keep flipping the PRV manual lever (it's there for a reason, for flushing out the valve) until it stops leaking. The valve seat seems to get sediment on them. It's a messy process but works- unless the PRV is just too old.Once I had air in a system and it was because the system pressure went too low, the water pressure regulator had jammed. So I hit the regulator a few times and it started flowing. Or manually (like you did) open the bypass valve until the system pressure goes up to allow the air to be bled. Note this fixes nothing because the pressure will slowly drop and ultimately the regulator needs to do its job.This winter is a strongLa Niñawhich means some brutal cold snaps up north, so I would make sure everything is working good.

author: MathWizard
author_rank: Super Contributor
timestamp: November 16, 2020, 12:15:39 am
content: Well it seem's to have stopped leaking, the pipe it completey dry at the end, and the upstair's has flow. So I'll just remind the people upstairs to bleed their radiators more often.But for the last 20 years, I've wanted to know way more fluid dynamic's, I did a few equations in high school and uni, but I never memorized any of them like gravity or even EM. But now I know more math, so it show be about all the same ODE's and what not.Now if I could only figure out how to derive multi-vibrator eqn's, like LTSpice can do, I could get some where.

author: Ian.M
author_rank: Super Contributor
timestamp: November 16, 2020, 12:37:31 am
content: Your country flag says 'Canada', so what's the exterior temperature where you are? If the relief pipe has a significant length exposed to exterior temperatures and its below freezing it could be dry because its blocked with ice, which would be extremely dangerous as then you are one fault away from a furnace explosion!