Confused on dripping pressure relief valve on water boiler

Snowmelt

Today my uncle calls me and says his pressure relief valve on his boiler was dripping water. ( he told me Saturday at diner). I said no problem go to the supply house and get an expansion tank and another pressure relief valve. We changed them and the pressure relieve valve. Still wasn’t working. We installed a 40 psi relieve valve and it dripped before reaching 160 degrees. Make a long story short we changed the air separator and it worked. There was no clog between between expansion tank and air separator.does anyone have a theory on what it could be?

Jamie Hall

The expansion tank is either waterlogged, otherwise failed, or valved off.

hot_rod

Is there a fill valve? It could be over pressurizing the boiler

30 psi is the most common relief valve setting

Snowmelt

Jamie, no shut off on expansion tank, also my uncle just put a brand new one on before I got there.
Hot, I shut the fill valve off , I looked at gauge ( I know it may not be correct but I think it may be close) I put a new p.r. Valve I put to 15 pounds. Before I changed the spiral vey, by the time it reached 150 it went off on 40 psi.

kcopp

What was in for a separator? Sometimes if the nipple goes in too deep it will block off the entrance to the expansion tank...

EBEBRATT-Ed

I suspect you have a bad gauge. Or the new expansion tank is bad and has no air charge in it. Its best to check that before installing

mattmia2

What is the cold fill pressure? Did you set the precharge of the tank to that before connecting it to the system? What kind of system is it, what is the total system volume?

RayWohlfarth

@Snowmelt I had a similar problem and found the piping to the expansion tank plugged. One of the ways to test is to watch the PTA gauge when the boiler fires. If it slowly creeps up, the piping may be plugged

Snowmelt

like i said I changed the air separator and it worked.
kcopp that sounded good but it was working for about 3 or 4 years. before this happened

hot_rod

It could only be a couple failures. Either a fill valve, or tankless coil is over-pressurizing, or the expansion tank is not able to do it's job, waterlogged not properly pressurized or undersized.

If the same size tank worked in the past, eliminate that.
I don't think you have a tankless coil?

Shut off valves can fail, leak slowly, maybe loosen the union on the fill valve to assure it is 100% off.

That leaves you with an expansion tank, or connection/ piping issue.

No valve or plug in the expansion tank piping?

Now you have two options, tank is waterlogged or under pressurized.

We have heard of diaphragms sticking in tanks, not allowing movement or flow into the tank.

Snowmelt

Hot rod, tank is the same for last 25 years. I replaced it and still leaked or should I say pressure on the gauge went over 40 pounds. No tankless coil or indirect water heater. (Boiler only)

Just to clarify the fill valve I installed 5 years ago with press fittings. My uncle shut that off to install a new pressure reducer. We made sure the pressure reducer was between 10 and 15 pounds with a cold start. The boiler stated and the t & p valve still leaked. I ran all three zones, when it reached 160 degrees the pressure went a little over 40 pounds. We watched the temp go up to 190 degrees when aqu stat was set for 160. So we changed that also.
Still same problem, only thing I didn’t change are the old style flow checks. And the air separator. The flow checks close and opened properly so I eliminated that.
Only thing we didn’t change was the air eliminatior, it was the spiril vent jr. we changed it to the taco 4900. Filled the boiler back up with cold water re blead the zones, made sure the boiler pressure was at the 12 - 15 pounds.
Then it worked. But why or who could explain why or how the old air separator clogged the expansion tank.
When I unscrewed the tank there was a little bit of residual water but not much..

hot_rod

With the tank disconnected from the system, was the pre charge checked and adjusted to 15 psi fill pressure?

Sure sounds like it doesn’t have much or any expansion function

Solid_Fuel_Man

Like hot rod I too have had a brand new Amtrol expansion tank diaphragm stick on commissioning. Pressure rose to 25 or so and then you could hear the diaphragm move and the pressure returned to near fill pressure. But 40psi is a lot more than 25 with tank aired to 12 before filling system.

Alan (California Radiant) Forbes

I can't tell you how many times this has happened to me. Increased the size of the x-tank and it still happens. Turn off the fill valve, replace the relief valve. Sometimes there's a clog in the piping, but most of the time it's clear. There's got to be another element in this formula.

neilc

do we have a full picture of this ?
with the tank off, how was it isolated ?
did you crack a valve and prove flow to the tank ?
or, and it's been seen here before,
with the zone valves shut, are they isolating the tank from the boiler ?
seriously, post a picture of the whole boiler and piping?

GroundUp

I just had a similar scenario a couple weeks ago. Set the tank to 12 psi and set static cold pressure to 12. By 120 degrees, suction pressure was knocking on 40psi. Did the math, engineer had too small of a tank by a few gallons but it wasn't enough to cause this much pressure rise. Fought it for 2 days and ended up going and buying a new tire gauge for the bladder as it was the only variable left. Turns out my old gauge was reading 12 when the actual pressure was almost 30, so the tank wouldn't accept any water. Started over with a dry tank and set to 12 again with the new gauge, and it hangs about 15psi hot now. Tank is still too small, but the engineer knows everything so that's what they get. In your case here, is it possible the bladder was stuck to the side of the tank and wouldn't accept any water?

mattmia2

Never use one of those tire gauges with the stick that shoots out for anything, they are not remotely accurate. Get a dial gauge or a good bike pump.

Could debris have collected in the spirovent and plugged the port in the bottom?

GroundUp

mattmia2 said:

Never use one of those tire gauges with the stick that shoots out for anything, they are not remotely accurate. Get a dial gauge or a good bike pump.

Could debris have collected in the spirovent and plugged the port in the bottom?

The faulty one I was using was a dial. I bought another dial one as well as a 1-20psi stick one and they both read the same now. I'll keep one in each truck

mattmia2

The dial type gauge has to be a quality gauge and you have to make sure you don't drop it.