Trouble with Pressure Regulation in my home heating system

castover

I had a leaky expansion tank on my heat system (radiators and in-floor heat on same boiler) and changed it out a couple of years ago and everything went perfect with pressure regulation doing exactly what I hoped. Then in the last few months it started to not work well with water frequently getting burped out of the system and then me having to add water. It's clear it is not functioning as when I add water the pressure spikes in the system.

So, I added some air to the 5 gallon tank (20 strokes on the bike pump) and it acts the same. A day later added another 20 strokes and it still acts the same burping water out the pressure relief valve. Can you experts please give me some guidance? Perhaps there is too much air in the expansion tank which I could imagine could result in the same issue as not having enough (but, how would it have gotten in there?). Not knowing the amount of air in the tank makes it hard to figure out. Perhaps I should let all the air out of the tank and then put a certain number of bike pump strokes in? Then I would at least have a number (# of strokes) that I would know is in there. Help!!!

STEVEusaPA

As said in the movie "Mr. Mom"..."You're doing it wrong".

If your expansion tank is leaking (I assume out the schrader valve), it has failed and needs to be replaced.
You check the tank by isolating it from the system, or drop the pressure in the system to zero, and checking the air pressure with a gauge. The pressure in the tank needs to be the same as the pressure you will have in your system when operating (probably 12 psi).
But your real problem may be the fill valve not seating properly, adding pressure to the system, air in the system, or if you have an internal coil, leaking coil-or a combination of the 3.
If you are replacing the tank, get a Webstone expansion tank valve to facilitate easy checking/replacing without draining the system.

EBEBRATT-Ed

Yes as @STEVEusaPA mentioned you have to isolate and drain the water pressure off the expansion tank or remove it from the boiler to check the air pressure