I happened on your site as I worked on my boiler (baseboard heating system) as I had to fixed a burst pipe.
I always kept the water valve closed (what I mean is not the auto feeder but turn the main handle until I close any water from entering the system) and manually added water. And since the boiler was drained I also replaced a Bell and Gosset pressure reducer auto feeder valve that was there since I bought the house 20 years ago with a Watts factory set to 15 psi.
While at it I replaced the expansion tank ( Water Worker, tested and get about 12 psi), auto air bleeder valve (Taco HY-Vent) and the blow valve (Watts set at 30psi). I kinda wish I had also changed the pressure gauge.
I bleed the system, and I have heat in all the 5 zones. All seems good BUT, i still need to keep the water valve closed. When I turn the water on I hear the water filling and I do hear it stop a certain point (which makes me think the Watts pressure reducer and fill is working) but the pressure gauge was reading 40 psi and the blow valve did not release.
Made me think the gauge is faulty. It has been on the boiler since I bought the house and God only knows how old it is.
I tried this stunt while the boiler was actually running and water temp at about 180. I also noted that when I have the water closed off completely the pressure gets really low and sits at or close to 0.
Boiler running as well. I add water manually (slowly) and the pressure shoots up quickly to 20 psi and I shut off the water.
Then when it runs the pressure gets close to 30psi.
The blow valve does not blow but I worry that it will so i let out some water and then the pressure drops fast again.It now seems to be a bit steadier right now.
When cold its about 1-2 psi (looks almost at 0) and when running and water hits close to 180 its at about 22 psi.
I did try to leave extra water in the system (added and closed the water off) starting at 20psi (assuming the gauge was off) i came home from work and found a little water had released from the blow valve.So I took water out of the system and now its working OK for a few days.
But still have not opened the water valve.
At this point it seems best to leave things as they are. I am concerned about it possible running at no pressure as I had found it (but believe there is enough water in the system and is not dry).
Here is why I keep researching and looking for answers and why I am writing you this novel!
I cannot figure out why the pressure increases so much when I turn on the water and try to let the Watts reducer fill valve do its job and stop water from entering at 15 psi as it is supposed to do. I do think the Valve could be set wrong or is just plain busted right out of the box? I am naive enough to hope that a new one would works as it is supposed to.
Is there something else that could be causing it? Maybe everything is good but the gauge is not working right? It just seems I am back to the way it was before the pipe broke and had all my old parts on.
I still have to keep the water off and manually fill it if the pressure drops.
I cannot find any leaks that I can see. Can't vouch for any pin holes in the pipes that are behind the walls. Any bleeder valves that I found seem not to be leaking either.
Sorry to write so much. Just maybe you have something that I have not thought about. I can always wait until the end of the season and replace the auto reducer with another brand and see if that works.
When you replaced the expansion tank, did you use the right size expansion tank? You can but a temporary pressure gauge to see whats really going on at Ace hardware or any plumbing supply
Just hook it to any boiler drain on the system to see what is going on. The fluctuation of pressure may be due to an undersized expansion tank. If you would like to send pictures of the boiler and pipes connected to It, I will have a look and see if I can see any problems.
I used a #30 expansion tank. I have a 2 floor home (no basement). The tank i replaced was the same size is was there. but to be honest I never really paid attention to the psi although I do know that it was fluctuate and during each heating season I did add some water to raise the pressure. I always that that was normal and I knew that the auto feeder was not working so I just dealt with it. Since I had to invest time this year learning more I now realize the psi should stay relative consistent and stable.
I will try the pressure gauge you recommend and see if that yeilds anything new and when i have the chance I will take some pics for you.
Last night I got home and there was no heat. mama mia! this time it was the Pilot light so I had to replace the thermocouple and got it to stay on again. This heating season has been fun and I am learning just about everything there is to know about a hydronic system!
But I am sure there is more! Thanks for caring!
Ok Well let me know how it goes and if you need any more help