: : While everything you say is correct -as always- I wonder if you are overstating the "danger". We are talking water heaters, not boilers. I would guess about a million people in the USA go on vacation every day, and maybe 1% of them turn off their water heater. Consumer devices, such as residential water heaters, are very conservatively designed. The T/P device and the expansion tank should be adequate protection.
: With regard to this particular customer, I wonder if there isn't some other situation going on. I don't know what it may be.
: Naturally, I would recommend following the manufacturer's recommendation to turn temp. down to the "vacation" setting.
Let the games begin (kidding)
Jimbo, your correct BUT suppose your in the 1% category?
As a Certified low pressure boiler and unfired pressure inspector I had the misfortune to be invited to Oklahoma as part of an accident inspection team for a school house explosion where several children had perished because of a "hot water heater explosion"
We found the cause was human error
Another explosion I learned about was a Korean Church and another in a Telephone building ALL were hot water heaters.
While attending refresher courses in OU (ASME) I learned one thing about hot water heaters the ONLY safety device if the T&P which rarely if ever gets tested.
A boiler on the other hand has several safety and operating controllers REDUNDANCY plus the Safety or relief valves also.
To trust a T&P a device that cost under $4, to protect against a possible explosion is in my opinion not very good odds even with the 1% factored in
Years sago water heater explosion was almost unheard of BUT then again there were no check valves or BFP on water mains so expansion had some place to go.
Today this is no longer the case so to make up for these short comings folks add expansion tanks or a watts type of ball cock ANYTHING to relieve pressure.
So if one removes the AIR it stands to reason the pressure will also decrease.
Jimbo, ever wonder why a high pressure vapor boiler (steam) is anything above 15# (PSI) yet a hot water (hydronic) boiler ASME section IV is rated 160 PSI and or 250 DEGREES.
Again, air can be compressed to really dangerous levels water wont happen OF course if a leak should occur @ 250 degree water temperature look out as it flashes into steam and kills everyone around the area.
So I only gave the Hoffman and turning down the temperature suggestions as a Boiler inspector looking how I would have treated a system I inspected.
If someone feels the 1% risk is worth taking needlessly go right ahead let them save the few shekels and hope they are not on the wrong side of the odds.
Are we having fun shooting this stuff around?