Help!! Boiler Pressure fluctuations

Brad White_9

for questioning.

From what you say, the symptoms seem to point to a "pumping to" scenario (which you state is not the case).

Next I would go to a compromized expansion tank, either in volume or bladder. The #60 seems a fair size (not like a #15 or a #30 versus a gravity system), so I would want to know if the tank bladder is defective. I know you said that you checked it, but that still could be masking the effect. IOW, if defective, how could you tell? Bladder pressure via the Shraeder valve with the tank removed?

This is what my first view leads me to want to check first:

1) If the system is at a cold fill, you could very well have 14 lbs. of static pressure even with a waterlogged tank.

2) When the circulator starts, it in effect might as well be "pumping toward" the PONPC.

Major Plummet in the Boiler Room with a Wrench is a, ah, Clue :)

Without an effective tank, this could be anywhere else in the system. Maybe trapped air at the top of some radiator?

3) When the system warms up, the pressure rises. Boyle's Law at your service. Pressure climbs as if little or no tank at all existed.

Another point which may be a Red Herring but raises my curiousity nevertheless is the bypass around the boiler. What regulates flow across this if anything? Is this to protect the boiler from low return water temperatures? If so it should be from the circulator discharge to the boiler return. The way I read it, the bypass is going from the return of the boiler to the circulator suction. Is that correct?

Brad

Paul Gibson

Boiler pressure fluctuations

We recently installed a Thermo-Dynamics HT 125-150 boiler in a residence. We've had repeated call backs with the homeowner claiming that the pressure relief valve is blowing off.
We checked all the usual suspects; Boiler feed control, domestic water coil, x-trol tank, and the relief valve itself.

In a recent warm snap we noticed that if the unit was running for hot water only the relief valve did not pop-off.

Today I went to the job myself and found the following
The boiler had a static pressure of 15# I asked the owner to turn up the thermostat. When the circulator kicked in the boiler pressure dropped to ZERO! The burner started and the pressure slowly climbed until it reached 30#.

We are "Pumping away"
The piping for the system is as follows.

Supply
-1 1/4" shoulder nipple
-Bypass piping to return
-1 1/4" x 24" nipple from the top of the boiler
-1 1/4" 90 degree elbow
-1 1/4" x 6" Nipple
-Watts air scoop with an automatic air vent on top and a 60 series x-trol tank from the bottom tapping (pressure set at 14#).
-1 1/4" x 6" nipple
-1 1/4" 90 degree elbow
-1 1/4" x 4" nipple
-Taco 007 circulator
-Taco 1 1/4" flow check valve
-1 1/4" isolation ball valve
-Existing radiation assorted cast iron radiators.

Return
1 1/4" isolation ball valve
1 1/4" x 6" nipple
1 1/4" tee with one end plugged
1/1/4" x 5" nipple
1 1/4" bypass piping to supply
1 1/4" x 6" nipple
1 1/4" 90 degree elbow
1 1/4" x 4" nipple to boiler

The boiler feed control is piped directly to the top of the boiler.

Any assistance or information would be much appreciated

Lurkin' Murkin'

Severe cavitation at the pump inlet - flow check valve not installed or functioning correctly?