I just stumbled onto this site and all I can say is "where the heck have you been all my life"!. Great questions and great answers! My question is what is the function of a Hoffman Speciality #79 air vent (check valve inside) I've had one on my +40 yr. old American Standard hydronic boiler and have never changed it out! What is it's purpose and how can I tell if its working or not? Thank you!!
The #79 air vent has a max. operation pressure of 75 psi. It's purpose is to vent air out of the system. As long as the system pressure is below 75 psi the valve will vent. When the pressure exceeds 75 psi the valve will remain closed. If it fails it will either fail open or closed. To put it another way: it will never vent (closed) or it will vent all the time (open). As long as it is maintaning system pressure and providing proper heat it is working. Excess air in the system will cause heating problems in the system radiators. I hope this helps answer your question.
The 79 used to make "sputtering" sound every so often but I haven't heard that noise from it in a long time. Also boiler is beginning to "knock" when its called for heat. Once temperature is reached, boiler flame retires. No more "knocking". Circulating pump continues to run until thermostats are satisfied and then stops. Stanhvac1, thanks....makes sense. I'm going to guess my expansion tank has been taking most of the pressure and the valve needs to be replaced.
Good place to start. Valve could be restricted but it sounds like it may be bad if you never hear it venting. Of course all excess air will migrate to the expansion tank and also cause knocks in the system. Let me know how it truns out.
Stanhvac1...here's an update. Replaced the Hoffman #79. (little sucker wasn't cheap, $90) also replaced boiler drain and repacked a secondary shut-off drain while boiler was down. I learned "on this site" the B & G, FB #38 pressure relief valve has an adjustment! I had no idea! The reason I mention this is when I fired up the boiler, the #79 began purgeing air immediately (moisture spot developed at end of copper relief line). She burbed and moaned a bit but eventually settledown. Noticed pressure was getting close to the 30 PSI level. Watched it for the next couple of days and noticed, at rest and cool, pressure was hoovering around 14 to 15 PSI. After loosening the top nut on the #38 and inserting a flathead driver into the screw and turning it "counter-clockwise" was able (by releasing water through boiler drain) to adjust the pressure to around 10.5 PSI. I can say at full call (3 zones opened) she hoovers around 24/26 PSi with a temp of 190/210. Very rarely does the Amtrol expansion tank get warm. I can actually say the boiler hasn't run this good in at least 15/18 years. This site is THE best for home owners who have a general understanding of heating systems and take a safe approach to addressing real concerns! Again, thanks for the advice and the help! Bring on the Winter! BTW...this boiler is the "original"... house was built in 1964. ..yep, 50 next year. Looking at new boilers....kind of scary...not sure if its a case of bad installs or just poorly built units but a lot of really upset end users. Hope I can keep this one going...keeping fingers crossed.
John, Thanks for the update. It is always good to know the advise helps some. Most of the time we do not get a response. Sometimes it is diffcult to isolate a problem by the information given so we have to assume and start with the basics. I am sure you know your system is not as efficient as a new one would be, However, if it is working properly and no major problems I am not sure I would replace it. The #1 reason for a new system not working properly is a bad install or inproperly sized system. The new systems are considerably more efficient than even a 10 year old unit (up to 90% verses 60%) so a smaller system will be required most of the time when replacing a 10 plus year old unit. Again, Thanks and good luck. Merry Christmas and wishes for the best in 2014.
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