Thermal Expansion

[focusit]

Well, here a new one. We just recently serviced a home with a thermal expansion problem. Of course the T&P was opening from time to time. We found that the T&P valve would release when a cold water valve would open. Seems strange? I can understand a valve slaming shut and causing a problem, but open? Use on the hotwater side seemed to have no effect on the T&P valve. Closing valves on the hot water side had no effect. (example: lady would flush her toilet and the T&P would breifly open…mind you this was when the fill valve opened..not closed) We installed a potable expansion tank on the inlet of the water heater. This seemed to fix the problem but still don’t understand exactly why it was going off when cold water valves opened.
All the basics were check. ie. electric elements, t-stats, water temp, check valves, etc. Note: she had a backflow at the curb and check valves on both the inlet and outlet of the water heater. Any input?

[jomeisterParticipant]

A third year apprentice should be able to answer this post.Lets see what tired plbg.has to say about it.Show us what you got tired.Should be know sweat for a person with 53 years experience.I will even give him time to check out the question.

[robertgfParticipant]

would a third year apprentice use the word know instead of no? just answer the friggin question

[SelgasParticipant]

I await the answer to this problimatical question with baited breath.

---

Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians

[Retired plbg1Participant]

With the check valve on CW side the heater had no place to expand so it went out releif valve, boy am I good. How about you Jomeister do you ever answer anything , must be you dont know anything. OOOOOO. Come on show us your skill.

[oscarParticipant]

Tired plbg,you are about as good as a third year apprentice,not as good,but about as good.

[oscarParticipant]

The problem occured when the cold side was opened tired plbg.The check valve has nothing to do with it.READ THE QUESTION YOU BIG NUMBSKULL.It didnt happen when the cold side was shut.Boy are you GOOFY,instead of “GOOD”

[jomeisterParticipant]

You see what I have been talking about ,Oscar?Not only can tired plgb.not plumb,he cant read ,”are” is that the other way around?

[bozoParticipant]

Well tired plbg.Still trying to figure it out? Stop and think ,put some of that 53 years of experience to work LOL

[racefanoneParticipant]

CONDAR, did you check the incoming water pressure?I have run into a situation similiar to yours and the cause was the water pressure was to high.Just a thought.Hey Jomeister,Bozo and Oscar, cut the crap.Your comments are getting old.Get over it.

[CondarParticipant]

Yes, we checked the pressure. Installed a guage before installation of the expansion tank. It runs around 50psig before thermal expansion and then around 70psig after. Of couse, stabling again at 50 after a valve has been open. Looks ok.

I was told by a local supplier that it could have something to do with the volume of water supplied. It’s piped with 3/4″ from the curb stop to the water heater. Another interesting note: the water heater is the last thing in line on the cold water side. He felt that a more than normal volume was rushing past the open line valve causing a “cold water hammer” on the water heater. I don’t believe it has/had anything to do with “normal” thermal expansion. ie. check valve blocking water from expanding thus using T&P.

---

The more you complain, the slower I work.

[racefanoneParticipant]

Condar,makes sense to me. Have a good one.

[Robert Stephen MortonParticipant]

Condar. if that is the problem why dont you install a pressure limiting valve to that unit, you could check by installing a pressure guage at the hws & see what happens when the cold water taps are used.
Bob

[Author]

Posts