Originally Posted by lewster
IIRC, an annual cleaning is required with vinegar. It's almost 100% ignored!! You can find the small print in the Atwood owner manual.
I went through the Atwood XT owners manual, and the only mention of vinegar cleaning was to get rid of Hydrogen Sulfide smell. Is there another place I should look?
It's very possible that Atwood's legal department, in their infinite wisdom, deleted that section. The last time I saw that was a bunch of years ago when the XT water heaters first went into use and I first encountered the hot water flow problem in an SOB 5th wheel. Customer couldn't believe that the tempering valve was the problem, and I looked over his owners manual and found the clause, which is obviously now AWOL. It also explained how the tempering valve operates and why keeping it calcium and corrosion free was important.
I am intimately familiar with the use of tempering valves that are used in a similar situation. Aqua-Hot hyrdonic heating systems, which are diesel-fired hydronic heaters with an integrated tankless water heating system, use these type of tempering valves, although they are made by Honeywell and not some unmarked off-brand like the Atwood units and are of much higher quality, but not more expensive!
Depending on the water quality flowing thru these Honeywell tempering valves, they last almost indefinitely, as I have replaced only about a half dozen valves after servicing over 2000 Aqua Hot units. They temper the 190ºF water coming from the Aqua Hot units to a safe recommended setting of 120-125ºF. These valves are also adjustable so you can crank up the water temps if desired, to a maximum of 140-145ºF. The biggest difference here is the tankless operation of the Aqua Hot with virtually unlimited available hot water, where the Atwood XT is trying to give you more hot water capacity (8-9 gallons from a rated 6 gallon unit) by super heating the water.
One of the great things about DIY
is the fact that you are free to do as you please with any appliance that you have in your RV, whether it is de-listing it by unauthorized modification or simply deleting factory engineered safety equipment. I won't and can't make suggestions to that end due to professional liability, but as always....YMMV!