Boiler low water pressure. Uggh...probably simple but..

[Woodyses]

I have a WM oil fired boiler with hot water coil.
We had low pressure on the hot water at all faucets so we replaced the coil. (Still low pressure at faucets)
Now my issue is the boiler pressure is toping out the gauge! (Relief valve not poping either so probably need to replace that)

If I shut off the supply and drain the boiler down to the proper pressure it holds but as soon as I turn the supply back on the pressure climbs right back up.

It has a Bell and howell fb 38 pressure reducing valve on the line in.
What's going on?
Im concerned with the boiler pressure first

 

[Dana]

Make sure that the expansion tank isn't shot, and is properly pre-charged to the system pressure before pressurizing the system.

If the pressure is creeping up over time there is either seepage at the pressure reducing valve, or leaks at the coil. Sounds like the Bell & Howell auto-fill PRV is either sticking or seeping. It's fine to bleed the pressure to the right level and NOT turn the supply to the boiler on. Hopefully the potable feed to the embedded coil has it's own valve? With the boiler isolated from the supply if the boiler leaks and pressure drops it'll start making a lot of whining sizzle clanging & banging from micro-boil at low pressure long before it becomes a true hazard.

 

[Sponsor]

 

[Woodyses]

Make sure that the expansion tank isn't shot, and is properly pre-charged to the system pressure before pressurizing the system.

If the pressure is creeping up over time there is either seepage at the pressure reducing valve, or leaks at the coil. Sounds like the Bell & Howell auto-fill PRV is either sticking or seeping. It's fine to bleed the pressure to the right level and NOT turn the supply to the boiler on. Hopefully the potable feed to the embedded coil has it's own valve? With the boiler isolated from the supply if the boiler leaks and pressure drops it'll start making a lot of whining sizzle clanging & banging from micro-boil at low pressure long before it becomes a true hazard.

Thanks! Was able to determine the reducing valve is shot...and a cruddy expansion tank so I will replace both Saturday. That should solve the problem then I can move on to the next problem/problems!

 

[Dana]

Unless it's an unusually tall 2-story or a 3 or more story house, set the PRV to 12psi, and pre-charge the expansion tank air to 12-15 psi before installing. Don't just assume that it' all correct just because that was the stated factory pre-set in the literature.

Even cruddy looking expansion tanks can still be perfectly functional. Assuming it's a bladder type with a schrader valve (tire valve) on one end, tap the air-valve end with a screwdriver handle- it should be a "ding" rather than a "thud". If it's a thud it could either be a failed bladder, or it's lost all of it's air charge. That can be tested by pushing in the center of the air valve- if water comes out, it's junk. If it hisses or is quiet but no water comes out it may just be a leaky air valve, which is a $3 repair, and to be pre-charged to the system pressure (or a few psi higher).

Tankless coils are a PITA with comparatively poor hot water delivery even when working well. That may or may not be related to your poor flow problem on the domestic hot water. An indirect fired tank heater can deliver 10 gpm with ease, and set up correctly will improve the overall efficiency of the boiler. But since you've already sprung for the replacement coil AND installed it we'll just try to make it all work as well as possible.