For starters, I can only guess since I can't see it from here.

The 'TP' valve is a safety. That's it. If it blows off, you have a
problem. It could possibly be trouble with the expansion tank.

"Linc Vannah" wrote in message
m...
Thanks for the response, HeatMan. If I had a pinhole leak in the heat
exchanger, why would I only see a rise in boiler system pressure when
I turn off the city water supply valve?

Thank you,

Linc


"HeatMan" wrote in message
. net...
"Linc Vannah" wrote in message
m...
"HeatMan" wrote in message
link.net...
How do you heat your domestic hot water? Is it a coil inside the
boiler?


Yes, the domestic hot water is heated by a coil inside the boiler.

Linc

That's most likely your problem. You have a pinhole leak in the coil
and
it's causing the pressure to increase inside the boiler.

You possibly can have the indirect coil replaced, but I'd recommend
either
an indirect tank or a separate water heater.

For someone that really knows wet heat, check out this link.
http://www.heatinghelp.com/getlisted.cfm