On February 7, 2013 I received and installed this Rheem tankless LP water heater RTG-64XLP, rated at 155 GPH.
Our former Rheem PTG2-42PVP was rated for 122 GPH which turned out to be somewhat limp.
The next day, after connecting the water lines and the twin-stage 525,000 BTU regulator which leads to a 100 Lb propane tank, I connected a Home Depot power cord. The story of this regulator is described in detail at Adding some muscle.
This entailed removing one bolt from a steel shell that is attached to a steel mounting plate, itself attached firmly to the body of the water heater by two bolts. All three threaded male bolts and female threaded receptacles are solidly engineered connections.
A pair of wires hung free from the mounting plate. The new power cord was connected to those wires with wire-nuts. Its green grounding wire was attached to a green bolt also firmly imbedded into the mounting plate. The steel shell was then reattached to the mounting plate with its own bolt.
This procedure was carefully depicted in its own web page at Disassembling A Rheem RTG64XLP.
Half way down that page it also describes a leak developing in December, ten months later, as a result of a freeze-up and power loss. Rheem sent me some new parts. Installing those required removing just about everything else, if just to make room for my hands and tools. This included unbolting the fore-mentioned power box. When I put everything back together, it worked. Done!
Well, no; not quite. From time to time, it would not get and/or stay hot.
I occasionally found that if I just unplug the thing and plug it back in, we could get a hot shower, at least once. This may have included gently slapping the water heater aside its head now and then. We got used to washing the laundry in cool or cold water; it might begin filling with hot water, but that would not last.
On March 3 in 2015, about a year and a third after our last conversation, I called Rheem again in frustration. With the hot (not) water running in the sink, he had me look through the little window up near the right hand ignitor coil (there are two ignitor coils). No spark was visible.
The next day, a new ignitor coil arrived by FedEx. I replaced the right-side coil even though it appeared to be just fine.
However that did seem to fix it, until …
On April 5 in 2016, a year and a month later, a similar story is described in that year's journal at Hot Bot, Not. That iteration involved a lot of cleaning of ignitor coils that in fact did not appear to need cleaning.
Incidentaly, those blocks of wood that you see on top of the water heater are there to keep our local doves away. One year they did put a nest of dry twigs up there which is probably not a good idea. Likewise our clothespin basket which we no longer leave out there on the wall hook.
Then on November 23 of that year, again under the direction of a Rheem tech, everything got disassembled and blown out with canned air even though there was no visible dust.
There was a Mud Dauber Wasp nest at one end of the exhaust vent but that would have had zero affect of the production of hot or not water. However I did look very carefully for any other kind of nest or web inside and behind things.
BTW, I do give ten stars to these Rheem techs for their depth of knowledge (ie: excellent database) and their casual breadth of patience.
Three lessons were learned here:
Buy the stronger version of canned air.
DO NOT disassemble the burner assembly unit (as I did) no matter how tempting it is to see inside. You do not have enough fingers or patience to put it back together. You could damage the parts. Blowing it out with air is all you need. Also there is nothing inside that you can't see from the outside.
However if you do end up with a box of parts that refuse to reassemble, then to save your marriage Google recommends ComfortGurus.com (item RTG20212D) for $180 plus. I am sure Rheem can also sell you a new one. Call them at 1-866-720-2076.
After all of the above, the solution; the nirvana; did finally come in a moment of DUH! head-banging introspection:
Bolt the damn power box down so that it is firmly electrically grounded; don't leave the box just conveniently floating around where it sometimes touches metal, and sometimes NOT!