On Friday, January 8, 2021 at 7:49:24 AM UTC-5, micky wrote:
In alt.home.repair, on Fri, 8 Jan 2021 03:25:44 -0800 (PST),
" wrote:

I noticed the pressure on our Utica MGB125hd boiler was up around 40 psi.. I was concerned because I read that the range for a gas boiler should be between 12 and 30 psi.

I bled one of the radiators and there wasn't any air but I noticed the pressure went down a bit so I let a little more water out from the radiator at the bleeder valve and the pressure went down some more. I probably let out about 10 ounces of water from the system.

It is now running at 27 psi when hot. What would cause the pressure to go up like this?

The boiler is about 20 years old. I asked the manufacturer how long they are supposed to last and they told me 18 years. I am thinking maybe a faulty relief valve somewhere. I would appreciate any thoughts on why this might have happened.
It should be possible to find any relief valve. Did the manufacturer
help about that?

Do you have the manual?
https://www.manualslib.com/products/...5-3549263.html

I know this site and it's safe, but are all the manual sites safe from
malware? This one has no advertising that I recall. How does it make
any money? It doesn't claim to be a public service.

It seems to have 3 copies of the same thing, although they are 1, 2, and
4MB!!!

It says " Cast Iron Gas Fired Boilers For Forced Hot Water" Isn't hot
water pressure handled just by a pump, so why woudl bleeding water lower
the pressure?

Because it's a closed system, with a one way valve that allows fresh water in but not back out.