Water Heater Excessive Pressure

[Roger Dowdy]

Hi All. My first post. Hope I post correctly.

My daughter complained of her hot water heater pressure relief valve leaking and asked that I replace the valve for her. I checked her house water pressure with a gauge at 60 lbs. Opened a bathroom hot water faucet, attached a hose to the tank drain valve, shut off the cold water supply and drained a few gallons of water from the tank. Checked the water tank pressure at the drain at the bottom of the tank to ensure pressure was off the tank then measured the air in her expansion tank. It was 15 lbs. Since I was suspect of the expansion tank and it was about 7 or 8 years old I bought a new one and with the new tank on the tailgate of my truck aired it to 55 lbs pressure, installed it, turned on the tank supply, put everything back to normal and went home.

Checked with her about two weeks later and all was good...no leaks from the relief valve. Couple of days later she called and said the relief valve leaked again one night. I went to her house found house water pressure good and no leaking. I put a water pressure gauge on the drain port of the water heater ( gas turned on and the heater in it's normal operating state and it showed 60 lbs pressure. Left it on the heater and asked her to monitor. About a week later the gauge showed it had been as high as 100 lbs. Went to her house yesterday after about a week additional time and the gauge showed it has at some point been as high as 150 lbs. which is the trip point for the relief valve. Current tank pressure at that time was 60 lbs.

What the heck am I missing? I thought of a stuck thermostat but
they haven't noticed any excessive hot water temperature in the house. Why would tank pressure rise that much just "sometime". One note: the expansion tank yesterday still seemed to not be full of water ( just tapping on the tank, bottom sounds "thud thud" the top half "tink tink". ( forgive my amateur discription. Don't know what to do next. It still hasn't leaked from the relief valve in two or three weeks but the pressure has been up there at least once. One note: The expansion tank is a 2 gallon tank and her water heater is around 60 plus gallons ( if memory serves me). I guess that's too small but I went with what was on the tank originally because of concerns about how the expansion tank was supported.

Forgive the long epistle but I was trying to be complete with what I posted.

Thanks everyone.

RD

 

[Roger Dowdy]

A follow up! Went to my daughters house yesterday. Upon entering the garage where the water heater is located I immediately looked at the water pressure gauge on the bottom drain spigot. Both current and maximum needles were a little over 150PSI and there were about two cups of water from the relief valve in the bucket from the valve. I immediately tapped on the expansion tank and just from sound it seemed not to be filled with water. Went into the house and turned on a hot water handle in a sink. There was no sudden rush of water as I thought would be with that much pressure in the tank and water temperature was normal as judged by running on the back of my hand. Went back to the garage and the pressure gauge then read it's normal 60PSI. I don't understand what is going on. My daughter says the problem seems to occur when they are out of town on business for a couple of days. If one does not use water from the tank does pressure accumulate over time or does it only increase when water is heating then goes down as tank water gradually loses heat? I'm wondering if the air pressure gauge that I set expansion tank pressure with is accurate. May get another gauge and recheck it. I live over an hour away from her so guess we'll just have to get a local plumber figure it out. If I find or hear of a solution I'll share the information. Meanwhile if you have any ideas I'd love to hear them. I'm no plumber but I am curious.
Have a great day everyone.

Me

 

[FishScreener]

Water heaters can generate increased pressure from the expansion of the water as it heats. But a 90-psi increase is a bit extreme, and generally happens only when there is some kind of valve in the system to restrict the volume of the system, and keep it from escaping. Typically if you are on a well, the pressure tank is more than capable of absorbing the increase in volume, so you don’t need an expansion tank on the water heater.

Is your daughter’s house on a municipal water system? If so there may be a pressure reducing valve which isn’t sealing up tight as it comes up to the limit pressure, and is slowly letting more water into the system at a higher pressure, and the water heater cycling, is causing the pressure to go even higher.

 

[Roger Dowdy]

Thank you. You make an excellent point! Yes, my daughter's house is on a municipal water system. The water supply enters the garage thru a ball valve ( extremely hard to turn off ) followed by a pressure reducing regulator then the supply hits the expansion tank and inlet to the hot water heater. The pressure reducing regulator also tees off and feeds the rest of the house. My daughters house also has back flow preventers on individual feeds to the bath rooms, etc if that is a factor. I don't know the city water pressure before the regulator but cold water pressure on outside faucets was normal at 60PSI at the times I have measured it. I think I see your point. If the pressure regulator was at times intermittently passing excessive pressure that would explain why pressure in the tank intermittently goes high while water temperature seems normal. It may be worthwhile to change out that regulator just to see if that cures the problem.

 

[FishScreener]

A bad pressure reducing valve, with a slow leak definitely would explain why it is worst, when they haven’t been home for a few days. Every time they open a valve the system gets bled back to the regulated pressure. but, as the system sits, and the valve slowly admits more water, the pressure slowly comes up, as a function of the total volume of the system, and the rate of the leak.

 

[Roger Dowdy]

Thanks FishScreener.

As soon as I can make arrangements to return to their house I'm going to replace that regulator.

Me

 

[Diehard]

1. You should confirm the recommended expansion tank size based on the specific water tank size, the typical maximum service pressure and the maximum hot water temperature setting.
For example: 60 gal tank, 60 psi water pressure and 120 deg water temperature setting would typically be about a2 gal tank.
A slightly larger tank or 140 temp setting or a slightly higher water pressure would put you in the next tank size of about 3.2 gal.

2. The pre-charged air pressure should match you typical max. water service pressure. That would give you a little more volume to start with.

You can still replace the PRV.

 

[Roger Dowdy]

Thanks Diehard:

I chose a 2 gal tank based on that was what was already on the system. I have a feeling though that it should have been larger. I charged the expansion tank to 55 lbs based on 60 lbs pvr setting. Will be seeing my daughter in a week and will follow up with her regarding PRV replacement and take it from there. The thing may go a week or two at a time without the relief valve operating. Mostly happens when she is away for a day or two and little hot water is used. The water never seems to be excessively hot so guessing it is not thermal expansion but rather PRV valve allowing excessive pressure leakage? Thanks for taking the time to help.
Me.

 

[JHEARD]

Thanks Diehard:

I chose a 2 gal tank based on that was what was already on the system. I have a feeling though that it should have been larger. I charged the expansion tank to 55 lbs based on 60 lbs pvr setting. Will be seeing my daughter in a week and will follow up with her regarding PRV replacement and take it from there. The thing may go a week or two at a time without the relief valve operating. Mostly happens when she is away for a day or two and little hot water is used. The water never seems to be excessively hot so guessing it is not thermal expansion but rather PRV valve allowing excessive pressure leakage? Thanks for taking the time to help.
Me.

Any news?

 

[Roger Dowdy]

Thanks for asking and sorry for not following up sooner. My daughter gave a report today. Since I adjusted the PRV from 60 pounds to 55 pounds ( expansion tank already at 55 pounds) and adjusted her water temperature from "B" setting to "A" setting on the water tank the highest pressure gauge reading recorded has been 125 lbs on the water tank. I made the adjustment about two-three weeks ago. They have not been out of town during that time but thus far no leaks from the relief valve. I'm guessing that if I had installed a larger expansion tank on that 70 gallon unit it would not be so marginal. I have not replaced the PRV at this point. Will repost if anything changes. Thank you for your help and interest.
Roger