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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 21391
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have a Takagi Jr 2 that is about 4 years old at our

Customer Question

I have a Takagi Jr 2 that is about 4 years old at our cottage. Over the past year the hot water output has been intermittently turning off. It's been getting worse as of late, running from anywhere from 1-2 mins up to maybe 5 min before going cold. But now it won't turn on at all. The unit ignites for about 1-2 secs then the flame goes out. After three tries it throws an error code 12, flame sensor I think it's called. I have checked most of the troubleshooting items, cleaned the flame sensor, but makes no difference. Still ignites for about 1-2 secs and retries 3 times then throws error code 12.
I do not suspect propane as the problem as it is running off a 100lb tank which currently is full and all other gas appliances are running flawlessly.
I suspect it is the main pc board but would like to ask an expert first.
Thanks in advance, Steve
Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year ago.

Do you have the manual? Did you check the other possible causes in the manual?

Customer: replied 1 year ago.
I have downloaded the troubleshooting manual. Error code 12 flame loss.
1. Check high limit switch... Ok
2. Check gas supply... Gas Ok
3. Check gas pressure... OK
4. Check that the clear plastic tube connecting the proportional gas valve to the combustion chamber is
attached... Cannot find this tube. Maybe refers to a different model??
5. If the flame comes on for 1‐2 seconds but then goes
out, clean the flame sensor... Yes it does! Cleaned flame sensor using 220 grit sandpaper being careful to not bend the probe. Was not that dirty to begin with. Still same problem. No change.
6. The overheat cutoff fuse may have been compromised... Check continuity. OK
7. Check for blockages in venting, such as bird nests, animals, or trash... OK
8. PC Board fault or Gas Solenoid fault... Have not checked solenoid and unable to test board.
Expert:  Rick replied 1 year ago.

Are there any visual defects on the board, like a burn or discoloration? Does the burner ignite then go out or not light at all? If it doesn't light do you hear a buzzing/ticking sound when it should fire up? An visible leaks from the heat exchanger? did you check for broken wires/bad connections?

Customer: replied 1 year ago.
Cannot see any visual defects. The burner does ignite but then goes out a few seconds later. Visually everything looks perfect.
Expert:  Rick replied 1 year ago.

Could be a bad flame sensor rod. The next step would be to replace it. It's unlikely but if the burner is clogged near the flame sensor that could be causing this.

Customer: replied 1 year ago.
Ok. I will order one and get back to you. I only have weekends to work on it as it is at our weekend cabin.
Expert:  Rick replied 1 year ago.

If the burner hasn't been cleaned/checked in a while you should do that first

Customer: replied 1 year ago.
I have already cleaned it. No change.
Expert:  Rick replied 1 year ago.

Ok, if you're sure about the connections then you're down to the sensor or the board.

Customer: replied 1 year ago.
Do you know what the voltage is supposed to be coming back from the sensor when the flame is on?
Expert:  Rick replied 1 year ago.

Typically 4 to 12 micro amps. Note that's micro amps not milli amps

Customer: replied 1 year ago.
not really measureable.
Expert:  Rick replied 1 year ago.

It is measurable but you need a meter that can read micro amps.

Customer: replied 1 year ago.
Thought I might have found it. A slightly corroded connection at the probe where the wire attaches. Started working again, but now it's back to how it was a few weeks ago. On for a few minutes then cuts out. Then back on again. Then cuts out. No errors.
Expert:  Rick replied 1 year ago.

Given the extremely low voltage signal from the sensor the connections must be flawless. the behavior you describe, in light of past errors, still indicates a flame rectification issue. Since you don't have any errors showing now it does cast more doubt on the board. But if you don't have a meter that can read micro amps I'd replace the flame sensor rod primarily because it's a lot cheaper than a new board.

Customer: replied 1 year ago.
I think I'll buy both. It may be the sensor but I also know the board is problematic so either way I'll have a spare of one or the other. I'll have to let you know how it goes in a week or so.
Do you have know of a preferred supplier preferably in Canada?
Expert:  Rick replied 1 year ago.

I'm in NH, I don't know any suppliers North of the border.