Takagi H3M-DV-N 100 Error 941

Andrew_D

I recently installed a Takagi H3M-DV as part of my shop in slab heating system, its a closed loop setup, 3 x 300ft 1/2" loops in concrete. 2" XPS foam under the concrete. The system has been in place about 6-7 months, and has worked well, no problem heating. I went out the other night and the system was not heating, the Takagi had an error 941 on it, which seems to indicate an abnormal exhaust temp. I opened the unit and the unit has some scorch marks under the burner and some chared paper in the case. I opened a case with Takagi (AO Smith) and they've basically said sorry, not for closed systems (the unit does say its supported for heating in open systems). I recognize its not a true boiler, but know many successfully use this heater for Radiant purposes. Any idea whats going on?

I've attached pics of the system.

DYI

I noticed that the vent piping does not conform to the installation manual. The manual states that for 2" vent installation 2" PVC is used only on the exhaust connection with a 3" PVC el connected to the intake from the room. Nowhere in the manual is 2" PVC shown for the intake connection.

For 3" vent installation 3" PVC is used for both intake and exhaust.

Andrew_D

I can definitely change over to 3" venting and intake, the unit is mounted on the back wall of the shop, and vents/intake right out the back wall, probably 1ft total length on each.

I figure I'd also add the grundfos pump runs around 2-3 gpm, and the temp is set for 105 degrees.

DYI

I would suggest one change at a time. Make one change and see what difference it makes before making the next change.

silverlex

I wanted to follow up, takagi is going to reluctantly replace this unit. I personally think it has a defective systemboard or fan. I will replace the venting per the feedback here though.

Andrew_D

Well - Replacement H3M-DV-N installed and lasted not quite a year Now showing error 341 which is for a thermistor failure. I opened it up and same type of overheat issue (scorched wiring and glowing red hot when running). This unit claims to be used for commercial use, can heat water to 160 degrees (I had it set for 120). It sees relatively little use.. .what gives? I know takagi doesn't rate them for radiant use (although the manual provides specs on using glycol and a heating diagram so take that for what it is). Are these units just junk? I thought Takagi had a good reputation. System was running 40PSI and seeing roughly 2gpm, with a 50 degree delta on in/out temps. Any recommendations for a small tankless or boiler that won't burn up every 6 months? Located in Kansas, aprox 30k btu load for in slab radiant.

Oliveone

wow that not a good sign that it gets that hot

kcopp

A tankless water heater is the wrong application for radiant floor heating.
Its not designed to have water RE-circulating through it. 40F in 120F out...
You really should have a boiler.
A modulating condensing boiler would be the best option.
I like the IBC HC unit. prob the 13-50 would work well for you.

yobi

Hi, installed same heater in March 2022 and 5 months later (last week) got the same issue. Called takagi and getting replacement. They made me open it and asked abount abnormalities, saw melted connector and right away they decided to replace the unit. I'm very worried about this unit for the future.

Looks like there is an issue withe that heat exchanger. Should bo on recall.

yobi

GGross

@yobi
Are you using this water heater for heating DHW or for space heating or for both?

yobi

For heating DHW only.

pedmec

regardless of weather that is used for heating or hot water this type of failure should not be happening. your lucy that you have seen it. how many are out there that are out of sight, out of mind. these units should be recalled immediately

yobi

@pedmec
Couldn't miss it, heater would throw 941 error ( no how water) and Takagi support made me open the unit, saw some partially melted connector and burned wire ( based on that they decided to replace unit - had a feeling that went to easy - they must of be aware of that issue) and when unit came on saw that hole in the heat ex-changer, and heat it blasting through it - FIRE hazard. As you said : these units should be recalled immediately.

pedmec

You got the error code before something serious could happen. That hole didn't develop overnight. It looks like it was cooking from day one.

yobi

Hi All,

just to update you all on this, my replacmet unist lasted about 6 months and same isue occured. Just got off the phone with Takagi and gettign seconde replacment. They say could be high gas preassure etc but are willing to send another unit, so clearly its an known issue - they should recall those units due to safty hazard.

GGross

@yobi

What type of fuel, and what is your incoming gas pressure measured at the unit when you installed it and after your first failure?

pepponyc

I have same problem. I dont think it is gas pression. This is a defective design. I have tried to contact Takagi to get a different model and free installation but they dont answer or reply to my messages. My lawyer is taking the lead on this case. Enough. I have been without hot water for more than 2 months now. Imagine the discompfort during these winter months.

Peter_26

I have owned one of these for 6 years now and have not had one single issue. The unit has been used strictly as a water heater. It has been flushed every year since install.