HWH T&P Valve Hissing (?)

D107

2006 Buderus G115-3, Riello 40F3, Logamatic, ST-150 Indirect with Watts 40XL-5 T&P Valve. Elderly resident reports hissing sound coming out what seems like the HWH relief valve. Lasted intermittently over about ten minutes, maybe ten seconds each time. Initially heard from about ten feet away. No water discharge visible. Everything functioning normally and no recent work done on system. Has not recurred to resident's knowledge since yesterday.



Boiler Tridicator gauge temp 120 and pressure reads about 15, according to resident. HWH taco 5000 mixing valve set to mix from 140 down to 120 for house. Logamatic set to heat HW coil to average temp of 140--not counting cut in cut out differential.



Online info says: "A properly functioning hot water tank will occasionally release water through a short pipe connected to the release valve. This can cause water to collect near the unit, but does not necessarily indicate any malfunction."



If this is as described, then I have no explanation. I thought of other explanations for the noise that have nothing to do with the hwh trv: auto circ exercising, boiler auto feeder adding water to system, hwh circ feeding hw into hwh coil. My HO two cents is that only the auto feeder might make enough noise to sound like a hissing noise. or possibly there were slight water discharges that weren't easily visible in the bucket.



Any thoughts? My concern here is safety of the system. Typically the Oil Co. doesn't like to test the PRV since they're afraid it won't re-seal and they'll have to replace it.



Thanks.

JStar

HWH

"Online info says: "A properly functioning hot water tank will

occasionally release water through a short pipe connected to the release

valve. This can cause water to collect near the unit, but does not

necessarily indicate any malfunction.""



This is one of the most ignorant and blatantly dangerous statements I've ever read. OF COURSE IT'S DANGEROUS!!!! A relief valve should NEVER release water. It's not okay. If it does open intermittently, it will usually rust itself closed, and turn the appliance into a time bomb. Hence, the DANGER.



I see relief valves as a one-time use item. Testing them automatically means replacement. The can never be resealed properly. So, the only way to test them, is to not test them.



As for the noise...you may be hearing condensation on start up. The flue gases may be producing water vapor which will steam off and sizzle.

D107

other possibilities

Thanks Joe. Since the boiler had not been firing, the 'sizzle upon startup' seems unlikely. Other possibilities might include: faulty valve, debris in valve, faulty hot water control or sensor that heats the DHW water above the usual limit. The latter doesn't seem likely, as by phone I got the boiler temp (162) and indirect hw temp (136) which are right on the money for being in-production of HW to raise it to 140. Acc to Buderus, boiler temp customarily goes up to 25 degrees higher than the DHW set temp of 140.



I'll try to get out to the house this week early in the day, flush the boiler and DHW valves and if there's any trouble re-seating I can call the oil co to replace. I haven't found a high incidence of re-seating problems, maybe only 20% of the time. And from now on, regardless of the oil co, valves will be tested annually as required.



I have seen suggestions online for the indirect once every few years to be cooled, and a hose connected to the lower drain cock to drain the bottom part of the tank to remove any collecting debris. A few years ago we had a tech open the DHW to inspect the anode rod and it was fine after 5 years.

kcopp

Is there a....

Potable water expansion tank on the Domestic hot water? If there is a check valve or a pressure reducing valve at the meter you could be getting expansion  and leaking at the T&P valve.

D107

Exp tank

Thanks, yes there is an Amtrol Therm-X Span T-12 expansion tank for the DWH, set at 75lbs I believe. Originally set 7 years ago; I'd like to have both boiler and DHW expansion tanks' pressure checked every few years but hard to find anyone to do it. Not sure how often recommended checking is. Upon installation in 2006, the first DHW T&P relief valve was the Watts 100XL which blew and they replaced it with the 40XL; been fine since then. Also, as far as reported, there has been no actual water discharge into the bucket below, only a hissing sound.