Odd problem with Gas Water heaters...

[nocturn]

Hi all.

I have 2ea, (1997 mf date) 50 gal State gas water heaters located in my garage. They both power a Apollo (aquatherm)heat system as well as the house hot water.

The past 2 nights, in the wee hours of the morning, BOTH heater's TP valves have blown dumping water through out the garage.

Yesterday I chalked it up to a water pressure surge and blew it off. Today, I'm a little more concerned. Here are the particulars:

This time of year I keep the gas on high at the heaters because its still quite cold at night. Anything lesser than 'max' and my gas bill goes way up because the h2o heaters would be cooking all day long. Outside air tems run 60 deg during the day/34 deg at night. The heat system is a split (1 up/1 down) and both zones are on a stat that shuts down the water pump at the air handler when temps are nominal.

Other appliances on the water heaters are: Dish washer, washing machine, and 3 full baths worth of faucets and showers. None of which are running when the TP's let go.

Seems really unusual that both TP's would fail on the same night. It makes me think something else is going one here.

Any direction on this would be appreciated...

Thanks, Randy

[Redwood]

I do not think your T&P valves have failed.
I think they are working exactly as designed to do.

A T&P valve discharges for 2 reasons Temperature & Pressure.
Most in a residential application will discharge at 150 Psi. or, at 210 Degrees F.

You need to take some tenperature & pressure measurements to determine the cause, Most of the time we see a discharge due to thermal expansion. Usually a discharge of about a coffee cup or 2.

Do you have a pressure reducing valve installed on your house?
Go you have an expansion tank installed on your water heater?

[nocturn]

Originally Posted by Redwood

I do not think your T&P valves have failed.
I think they are working exactly as designed to do. My thoughts exactly.

A T&P valve discharges for 2 reasons Temperature & Pressure.
Most in a residential application will discharge at 150 Psi. (which it is) or, at 210 Degrees F.

You need to take some tenperature & pressure measurements to determine the cause, Most of the time we see a discharge due to thermal expansion. Usually a discharge of about a coffee cup or 2. (Since its happened 2 nights in a row, Im thinking the same thing)

Do you have a pressure reducing valve installed on your house?
Go you have an expansion tank installed on your water heater?

No and No. I was quite surprised to find out the city does not require a PRV at the service entrance.

Ive never needed a ET in the past. Pressure has been a constant 55psi since day one. We have a city jockey pump located about 2500 feet from the house.

Maybe both WH stats are baked? Doesn't seem likely though.

[nocturn]

Wait a minute. I may have answered my own question.

Both heaters share a common water line between them. One unit (theoretically) can have a broken stat, over heat the water in not only its tank but the other also. Causing BOTH to over heat and both blow the TP...

hmmmm.

[Redwood]

Lets look at the amount of water discharged.

If the stat was bad and the temp raised tp 210 degrees the T&P would open full bore and discharge until the water was cold enough the reset the valve...

There would have been a bunch of water discharged...

I'm not saying impossible or, they wouldn't require that safety function...
But I am saying unlikely.

Take the measurements both temperature and pressure. See what is going on. i would use a lazy hand gauge over a 24 hour period to determine the highest pressure reached.



Post back with your findings...

[nocturn]

Originally Posted by Redwood

Lets look at the amount of water discharged.

If the stat was bad and the temp raised tp 210 degrees the T&P would open full bore and discharge until the water was cold enough the reset the valve...

There would have been a bunch of water discharged...

I'm not saying impossible or, they wouldn't require that safety function...
But I am saying unlikely.

Take the measurements both temperature and pressure. See what is going on. i would use a lazy hand gauge over a 24 hour period to determine the highest pressure reached.



Post back with your findings...

Will do.

The more I think about it, the more I believe it's a single bad stat. One heater is dumping HUGE amounts of water into the garage as I mentioned in my first post, while the other is dumping about 10 gallons. It only happens late at night so Im thinking the HVAC system is queuing hot water from the water heaters, the water heaters kick on after the hot water has been sent to the heat coils, the bad stat does not shut off when water temp is reached causing the temp to go up in both heaters thus causing the TP's to react.


I'll post my findings....

[Redwood]

Quite frequently water suppliers kick up the pressure as they refill tanks for the next days water usage.

[nocturn]

Quick follow up folks,

It was the themostat on heater #1. Stat #1 crapped out causing the heater to overheat the water, kicking the TP valve on BOTH water heaters. Heater #1 had 3X the discharge rate than #2.

I replaced both stats on both units and everything is nominal one week later.

Thanks to Redwood. Our conversation got me thinking.

[Redwood]

It's nice to have a smoking gun and know your fix is going to work...