Forced Hot Water Boiler Always Reads 25 PSI

[floodgun]

Burnham 205NC forced hot water gas boiler. Water, not steam. Two floors, three zones, using two Tacos, where two of the zones are covered by one of the Tacos. Opened boiler drain valve, water released fine. Purged all zones, no problem; lots of air as expected, then runs clean for each zone. Opened boiler PRV, some air came out for about 5 seconds then stopped, and no water came thru. Mystery is this: why do I still have 25PSI in boiler after doing all this. Is this an 'airlock' issue, or is my boiler pressure gauge bad, or something else? I would have thought either opening the boiler drain valve and/or purging would have brought it down to 0 PSI. Expansion tank is a 30 that rings at bottom and solid at top. Check valves are rusty and don't let anything through, but how could it be those if I purged the air out of all the zones?

 

[Fitter30]

Bad gauge. Take few pics of your system. Gauge shows temperature and water pressure and feet called a tridicator 1/2" pipe thread come in round, square shaped with piping out the back or from the bottom. Draining it down will be chasing air for a few days possibly and make sure pumps are off.

 

[Sponsor]

 

[John Gayewski]

First bet, bad gauge, second bet your full valve is set too high.