Boiler Question ?

Steve J_4

hello i wanted to understand something what happens when your exposition tank is set to 12psi and you fill your boiler to 19psi. what dose it do to the system? should the boiler pressure match the tank.?

thank you

Norm Harvey

In that situation the air in the expansion tank is compressed to match your 19psi fill pressure, taking up some of the volume of air inside the tank,.. when the water in your boiler is heated and expands the air in the tank compresses further and if there is not enough volume inside the tank to handle the expansion, your boilers water pressure will rise too much and you risk your relief valve relieving water.

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Steve J_4

okay because they have a second floor and when i purged the system i left it at just under 20 psi and the pressure never changed overnight at the boiler and the boiler dose reach high limit 190F

they said that the upstairs never heated so well and was quite as can be. no more banging. should i try dropping the pressure to 15 and see how that go's?

thank you

Ken_40

If the problem goes away...

at 20 # pressure, I'd bet lunch the circulater is "backwards" and located on the return, not the supply.

Is it?

Norm Harvey

if your boiler is at its 190 high limit and the pressure is 20psi with the circulator running, your fine.

The boiler isnt going to get any hotter, which means no more expansion.

The only potential risk is premature expansion tank failure.

As far as getting the second floor to heat better, a "pumping away" setup would do the system justice as well letting the circulator do some of the work to eliminate that air noise for you.

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Steve J_4

yes ken your right i put in a new buderus hot-water heater this weekend for them and the pumps where on the return and i cringed but it will only be for a few more months then i will install a buderus g115 boiler with 2107 and pumps on the supply with lwco spirovent and grundfos 15-58 pumps on the supply. so i will go over tonight and drop it down to 15 and see how it works

thank you

Norm Harvey

If the system is at 20psi when the boilers at its high limit (190) and the circulator is running, your not going to cause the relief valve to relieve water,...

BUT !!!

You only temporarily solved the problem.

As water weeps out of packing nuts and whatever, and the system pressure drops, your fill valve is still set to the 12psi which is inadequate apparently to heat the second floor.

I would recommend pumping up the expansion tank to match the fill pressure you need, and also adjust the fill valve to fill to that pressure.
While you have the expansion tank off and the system drained, thats a good time to do a small repiping job to a "pumping away" set up.

I would sell the customer on the repipe job.

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Steve J_4

what happens if we left it at 15psi for a few months till i take the whole boiler out and re pipe everything then. is it safe and okay?

because i don't want to go back there and try and sell that to him now when he told me he wants to yank out the boiler this summer.

thank you

Ken_40

You're on the right track

as long as you don't mind holding hands until the install (;-o)

Ken_40

15, or 20?

At 20, you might delay recontaminating the system with air. 15 is so marginally away from the 12 that's "standard"- I doubt it will keep it from getting air-bound again.

If it has an open expansion tank, you're dead meat. If its an Extrol type, you might be okay.

So many variables, it's a hard call.

If you have a substantial deposit and bona fide agreement with the client, I'd do whatever he asks. If merely a promise and hand-shake, I'd suggest he give you 10% minimally and change "summer" to: "The next forecast three days where the outdoor temps will not drop below 55F" as the contractually acceptable installation date.

The reason?

Summer may never come...

At least, not for you.

Norm Harvey

I agree with Ken. I posted before I saw your reply about the new boiler. So I would leave it at 20psi with the customer signing my invoice that states the problem will be recurring until action is taken to remedy the hydronics.





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