Takagi T-H3M-DV-N new install no-start troubleshooting

FlintMich · February 21

This will be long-winded because I'm hoping to include everything in my initial post in an attempt to minimize questions so please be patient. I bought this water heater for my shop back in August of 2022. Unfortunately it never got installed because of a lack of heat in my shop so, of course, the warranty is long since passed. I installed it myself so I would guess that any hope of a warranty went out the window there too. This is the third tankless I've installed and the only one to give me any trouble whatsoever. So anyway, I've recently installed it and I've yet to be able to get it to fire. Here's what I've done and what I "know" so far.

I keep getting a 111 code - which is ignition failure. My first diagnosis was no natural gas because the line from the meter to the shop had never been purged. I "assumed" the guy who did the final hookup would have done that - nope. So at first, I removed the screw in the gas port for hooking up a manometer until I could smell gas and tried again. Nope. Then I thought that maybe the gas in the1" line, running 100' was diluted by the air in the line. Even though I could smell gas, it wasn't an overly strong gas smell. So I threw the main breaker, killing all power in the shop, opened that port again and let it run until the smell of gas was nauseating. I then aired the shop for 2 hours with all the doors open, flicked the main back on and tried to fire a couple more times. Nope

I installed a manometer on the gas line coming into the shop and it shows 7+ WC so I'm good there. I pored over every troubleshooting manual and forum thread I could find. Not just for this model specifically, but Takagis in general and then some different brands. The following tests or checks is what I've tried so far…

I've read that during initial start-up, on this model anyway, I should hear 3 "clunk clunks", caused by the unit doing a pre-start check by opening and closing the electric gas valves. I can hear a faint clunking but nothing overly audible. I needed to know if the gas valve body was defective. I really cannot afford to start firing the parts cannon on this thing but I need to get it running.

When it tries to fire, the fan kicks on, it tries to fire 3 times and then the fan maxes out as it purges the combustion area. In an effort to understand what might be happening, I've tested for AC power at the igniter coil connection at the ECM. I get 120v+/- during the startup. I checked for DC power, at the ECM, going to the first main gas inlet valve. I noticed the clear air hose going from that electrical gas valve to the combustion chamber (check me on my terminology). My limited furnace knowledge tells me that this hose is a way to prove adequate exhaust gas flow in case of an obstruction. I even tried to gently blow and then suck on this hose during startup to see if it might make a difference. Nope.

All the manuals say this unit is reset every time it shuts down or power is removed. This unit plugs into the wall so it's really easy to reset. I've "reset" it dozens of times. Actually, every time it fails to fire, I unplug it and try something new. The manual says it requires 0.5 GPM to fire and the flow meter shows 3 GPM so no worries there.

Out of desperation, I removed the igniter / flame sensor / air-fuel ratio sensor plate, to allow me to listen and smell to see if ANY gas is reaching the burn chamber. Nope. So I'm now wondering, does the igniter need to sense the proper air-fuel ratio before the igniter will spark? Does the air/fuel sensor detect the ratio of unburned gas or is it more like a cars O2 sensor where it measures the burned exhaust? I ask because I've yet to see or hear the igniter spark.

I disconnected and then reconnected every electrical connector on the ECM, in case there might be a bad connection. Nothing. I did not unplug the 4 or 5 connectors on the back of the gas valve manifold because they are impossible to reach without a partial teardown. I suppose if I determine the gas manifold is the culprit, I'll try them too since I'll need to be in there anyway.

OK, I think I've covered everything I know about this issue, but I'm sure I've missed something. I hope it's something simple. I hate the thought of dropping $250 for a gas manifold on a brand new unit. Serves me right for not waiting until I was ready to install and then buy it so at least there might've been a CHANCE of a warranty. But you know how it is. I was in the heat of building the shop, the units went on sale, I had the money…. You get it.

So any help that anyone can offer is greatly appreciated. My fragile male ego simply won't allow me to call a service tech until I've exhausted every single possible option - lol. My man card is hanging in the balance guys. My son-in-law is watching. Have mercy on an old man and help a brother out. lol

Alan (California Radiant) Forbes · February 21

If you have confirmed getting a spark at the igniter and proper gas flow, can you tell if it ignites at all? If the pilot does not ignite, maybe the pilot valve isn't opening?