Is my boiler's PSI ok?

sputnik99

Long time reader, first time asking for help.

My house is 2 storeys with 7 cast iron radiators and the heating system is made up of the following:
- Gas Boiler (Slantfin GG100)
- Watts ETX-30 expansion tank
- Circulator on the return side of the boiler
- Single zone

On a cold start the psi is 12 and gradually goes up to 20 and pretty much stays there throughout the heating cycle. Is this normal? My expansion tank was precharged to 12 psi so I was expecting it to stay around that range. I ran the system without the fill valve by turning on the shutoff just before it and the backflow preventer. I also made some updates by replacing the expansion tank (it was waterlogged) and the pressure relief valve recently.

STEVEusaPA

Just checking, did you bleed the radiators?
Are you sure the expansion tank is large enough?

Ironman

Going from 12 psi cold to 20 psi hot is very normal. As long as you don't exceed 25 psi, it's okay.

sputnik99

STEVEusaPA said:

Just checking, did you bleed the radiators?
Are you sure the expansion tank is large enough?

I had bled all the radiators with the fill valve open then turned off the water feed and bled the radiator at the highest point to bring the pressure down to 12 psi.

I'm not sure if the expansion tank is too small. It's 4.7 gallons... I bought the same size as the previous tank which was in operation for 8 years.

EBEBRATT-Ed

Nothing wrong your fine. The expansion tank will not absorb all the expanded water. It is completely normal to get some pressure rise.

Check it once in a while like a few times a year. If you under 25 as @Ironman said your fine

sputnik99

Thanks for the replies eberatt and Ironman. I will keep an eye on the pressure.