Relief valve leak

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  #1  
Old 10-21-07, 04:31 PM
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Relief valve leak

I have a 25 yr old tankless oil burner with 3 zones. It's been running fine and has had regular maintenance. I've noticed that water dribbles from the relief valve on the back of the unit when one or more zones is heated. During the last burner cleaning, I had the repair man replace the relief valve. No change. The water heats to about 180 degrees, but I notice the pressure is slighly over 30 lbs.. about 35 lbs when the zones are heated. Its that my problem? What controls the water pressure? Thanks.
 
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Old 10-21-07, 05:04 PM
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Pressure is controlled by the autofill valve.

It sounds like your expansion tank is full of water. You will have to determine whether it is a precharged bladder tank, or a pressure tank (looks like a small drum stuck up in the floor joists.) Post photos and someone with walk you through how to recharge the bladder tank, how to drain the pressure tank.

I'm surprised the service tech changed the PRV without noticing that the system pressure was at max. Those PRV's are supposed to operate at 30 PSI.
 
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Old 10-21-07, 08:56 PM
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When you said "tankless", you mean there is a domestic water heating coil in the boiler ?

Basically, there are three things that can cause overpressure (which should probably be in the neighborhood of say 12-15 PSI when cold by the way).

1. As RC sed, expansion tank troubles.

2. Inlet water pressure regulator problem.

3. Tankless hot water coil leaking.

MOST of the time it's the expansion tank.

I'm not at all surprised that the guy just went ahead and changed the valve without even looking at the gauge, given the calibre of most of the techs today.
 
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Old 10-22-07, 04:31 AM
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Thanks... it is a bladder type expansion tank. Dom. hw is heated in the boiler. It seems that I have that expansion tank replaced every couple of years. Is that normal?
 
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Old 10-22-07, 04:11 PM
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Normal ? I dunno... I'm not gonna jinx mine by telling you how long it's been hanging there.

Before you change the tank though, you do need to do a few tests to determine where the fault is, because the problem could be any of the three.

What is the pressure on the boiler gauge reading when the system is cold ? You need to know this because if the pressure is in the neighborhood of 12 PSI cold, and it only shoots up to 30 PSI when it's heated, chances are it's your expansion tank.

It may not actually be defective, it is possible that it's simply lost it's air charge.

If the pressure is already at 30 PSI when cold, either of the other choices could be the culprit, and then process of elimination comes in.
 
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