Need (gas) plumbing guidance please - any plumbers on here?

[ard]

I might be pressing my luck, but after my fantastic experience with a fellow Pelican who went above and beyond to help me out when my pup damaged my stair tread, I thought it wise to turn here for help.

TL;dr: I am hoping someone can walk me through how to replace the water control valve on the left one of my tandem water heaters. It is the plumbing to tie the 2 water heaters together that is throwing me for a bit of a loop.

Background
This is the first time I have lived in a house with a tandem water heater setup. The house is about 9 years old and I am not the original owner. About a year ago the water control valve on the right unit went bad. I had a home warranty at that time and was able to get it fixed under warranty (how is another whole sad story - suffice it to say that it seems most warranty companies contract only with the 1-star reviewed outfits. It took several weeks to get it fixed, between the crews who couldn't execute simple diagnostics and the unwillingness of the warranty company to pay for the right fix and insist on trying "band-aids", but I digress; that experience is why I did not renew my warranty).

Recently the left unit stopped working. The LED stopped flashing. Even after re-lighting the pilot the LED began flashing 2 strobes in quick succession for a few minutes before dying off again. Per the manual that indicates a weak thermopile. I watched this pretty good IMO video on diagnosing Honeywell units and did my own tests. The pilot control valve appears not to actuate when 9V is applied b/w it and GND. I bought a replacement BNIB water control valve from Residio, which appears what Honeywell Home has rebranded itself into.

My ask
If a fellow Pelican with experience would be willing to talk me through / sanity check the steps I plan to do to undo all the plumbing to remove the control valve and the safety steps I plan to take, maybe via video chat, I'd greatly appreciate it. I am pretty handy with mechanical things but I am no expert in plumbing gas-fired appliances. I did watch a pretty good video by Roger Wakefield but he deals with a single tank setup which is what seems to be much more common.

I attached some pictures below.

Thanks for reading.

[gsxrken]

Alex, swapping out the gas control valve should be a straight remove and replace in reverse order operation, but you’ll need to make sure the water tank is valved off and the pictures don’t show all of the plumbing. You’ll need to make sure you’ve isolated the cold water inlet, the hot water outlet, and the recirculating loop that yours does appear to have. Then you can drain the left tank, spin off the old valve and spin on the new one.
Make sure you got the proper valve (natural gas or propane), other than that- good luck.

[ard]

Thank you for your reply Ken; very helpful.

I am attaching a picture of the top of the heater and I am looking for confirmation that this is the cold water inlet. I ask because even though there is a valve, the line coming out of the water heater is wrapped in pipe insulation and feels warm.

I have also added a picture of the recirculation system.

[A930Rocket]

I can’t answer your question, but I would think you would have two fill valves and two hot water valves on top. One for each water heater.

As far as insulation goes, they probably wrapped everything to keep pipes from freezing.

[Bill Douglas]

It's always cold water in at the bottom and hot water coming out the top. The top probably has a hot water expansion valve as well with a pipe attached that is cold because this valve is to stop the cylinder from exploding if the cold water expansion valve at the bottom fails.

The bottom one is so when the water expands as it gets hot it's cheaper to lose some cold water instead of hot water.

[dad911]

Service manuals here: https://www.bradfordwhite.com/professionals/usa-residential-tank-type-gas-ultra-low-nox/ultra-low-nox-atmospheric-vent-gas

Is that 2- 40 gallons or more? That's alot of hot water.....

If you have to cut the copper, and I think you will, sharkbites are your friend.

[Arizona_928]

interesting setup.

hot and cold water come out the top that is supplied to the house. that extra set of piping on the front; is an extra cold line to clean out the tanks (as normal maintenance). It's pretty slick. Looks like the PO attached an extra garden hose for utility.

That said. It's completely irrelevant to your problem. To change out the control unit you have to turn that yellow valve 90 digress (which you seem to have done already ie. the knob should be perpendicular to gas line) then disconnect at the trap on the left. The yellow hose uses an internal barb and does not take any sealant. The galvanized pipe always takes sealer. so when you put that trap on the new controller, you'll add sealer and use soapy water to check for leaks.

It's pretty simple, but you do have some extra stuff going on there.

[Arizona_928]

Should also mention. The heating control valve has nothing to do with the lines going into the tank on the top. It's literally just the burner assembly at the bottom of the tank.

[ard]

Thanks for all the replies so. I am having a busy week and will circle back to the responses later this week.

[ard]

First, thank you to the Pelicans who weighed in, provided helpful guidance and convinced me I would be able to tackle this repair myself.

The problem is fixed, and the gas burner now turns on when the control unit calls for heat. The mechanical part of undoing the gas lines and removing the control valve was pretty straightforward (Drain the tank first!). I had been worried about clearance between the control valve and the "tandem" plumbing line, but that did not turn out to be a problem, saving me the trouble of cutting and soldering copper pipes.

My biggest learning was that the gas valve control unit has to be matched to the specific water heater model. In retrospect that makes perfect sense but after diagnosing the problem to be with the gas control valve, I went online, entered the old model number and, per Resideo (which seems to be what Honeywell has rebranded its home product line to) found a new model which superseded my old one. However, after installing the replacement gas control valve unit I was unable to get the pilot to light. The self-diagnostics displayed via the LED indicated a bad control board. Since per my diagnosis the original problem lay with the main gas valve solenoid (and not the original control board), I swapped the original control board into the new unit. With that change, I was able to light the pilot via the trigger button, establish a flame, and bring the unit back to proper operation.

I'll give a shout-out to supplyhouse.com where I bought the replacement gas control valve for being very helpful over chat when I reported the problem to them. They collected the model / serial numbers of my water heater and original control unit, determined that the unit I had bought was not compatible with my water heater and pointed me to the correct one. Even though they said because I had installed the replacement unit and they therefore could not take it back, they offered to price-match the correct unit to the price I paid for the (incorrect) unit I bought. Given that buying the wrong unit was my fault I thought that was a fair offer.

The other "ugh" moment was that I could not remove the burner assembly clear of the water heater because the water heater is "set" in a large "tray" with a ~ 2" tall "lip" and a small pipe stub-out that directs toward the garage floor. That seems to be a preventive measure in case the tank fails catastrophically and discharges water, by directing it away from the walls. While that is a great idea, it seems to require undoing the wall straps and lifting and tilting the water heater to remove the burner assembly and I was not going to do that. I was able to pull the burner out far enough to clear of dirt and debris from the thermopile and confirm that I was able to spark the pilot with the trigger button.

Lesson learned - the specific water heater model and the gas control valve unit must be matched as a "pair".

[Bill Douglas]

Good skills.