Mhu75ng stopped lighting after about a year. Fan starts, but burner doesn't light. Fan stops after about a minute. LED code is 3 flashes. Gas supply should be good, heater in another room ups

Check for error codes and service manual on following link:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Replace gas control valve
http://waterheatertimer.org/How-to-replace-Honeywell-gas-control-valve.html

Gene:

Water Heater Timers Save Money

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

The set has a self check--try this(posted by another expert here):

"Here's something that might also be useful. After you turnon the set, and get the regular red blinky lights, hold down the Device andMenu buttons together for about 5 seconds.
The Power light will start to flash in a two digit sequence.
For example, 3 flashes, then 7 flashes = 37.
Here are the error codes, and the corresponding problem:
12 = No error detected, check power supply.
32 = Lamp Cover is open.
33 = Air filtercover is open.
34 = Lamp abnormality
36 = Light Engine (DMD or Lamp Fan stopped)
37 = Exhaust or Lamp Ballast Fan stopped
38 = Lamp Temperature High
39 = DMD Temperature High
41 = Short is detected
44 = DVI cablebetween FMT and Engine disconnected"

did you put a drip pocket on the line to the heater

get in a gas fitter to properly diagnose the problem,
igniters in ovens normally click / flash as that ignites gas quicker than a hot wire so I suspect that is problem 1
problem 2 indicates that there is a gas flow problem, probably a faulty hose or regulator
what ever it is , gas is not in the domain of diy so an accredited professional gas fitter is required to do the fix

the high limit is an over heat switch that could mean the unit is over fired. you would need to time input or check manifold pressure. the roll out switch is a switch that shuts the unit off if combustion is spilling at the divitor on the unit where the vent connects. with this you need to check your venting

Error Indication Information
Error No. Error Information ERROR DESCRIPTION LAMP LED OSD LAMP OFF
(Note 3) (Note 4)
POWER LED TEMP LED
Note:
1.When any of the above errors has occurred, the LED will flash as shown above every 5 seconds.
2.When two or more errors have occurred at the same time, the LED will light up or flash as shown above, and then
change to another every 5 seconds in turn.
3.Warning OSD appears when the Air Filter is clogged 90%, accumulated operation time of the Lamp reaches 5000 hours,
or accumulated operation time of the Air Filter reaches 400 hours.
4.LAMP OFF: The LED will flash right after the Lamp goes off.
5.IC2301 is mounted on LCD Main C.B.A. which is included in the Projection Unit.
6.IC6001 is mounted on TV Main C.B.A.
Clogged air filter
more than 90%
15)
16)
17)
18)
1)
2)
3)
4)
5)
6)
7)
11)
8)
9)
10)
12)
13)
14)
- flashes 5 times -
every 5 seconds
IC2301(pin82) detects the clogged air filter, then indicates the
error when the air filter is clogged 90%.
Front Fan stop or
Lamp Fan stop
flashes orange
once every
5 seconds
- -
IC2301(pin12) detects the Front FAN stop or Lamp
FAN stop, then indicates the error when the Front FAN
or Lamp FAN is stopped.
Lamp Cover open
Temperature Sensor
short or open
flashes orange
twice every
5 seconds
flashes orange
3 times every
5 seconds
flashes green for
140 seconds.
flashing red for
60 seconds.
light up red.
flashes once
every 5 seconds
flashes once
every 5 seconds
flashes red for
10 minutes
flashes once
every 5 seconds
-
-
-
-
Abnormal
Temperature
flashes twice
every 5 seconds
flashes twice
every 5 seconds
- -
Request for Lamp
Replacement - - lights up
Power Ballast Error
(abnormal
Lamp voltage)
- -
flashes 3 times
every 5 seconds
Power Ballast Error
(abnormal
temperature)
- -
flashes 4 times
every 5 seconds
Power Ballast Error
(other causes) - -
- -
Request for Filter
Cleaning -
Abnormal Voltage
on 16 V line of
LCD Main C.B.A.
-
flashes twice
every 5 seconds
flashes twice
every 5 seconds
Abnormal Voltage
on 14 V line of
LCD Main C.B.A.
-
flashes 3 times
every 5 seconds
flashes 3 times
every 5 seconds
Abnormal Voltage
on 7 V line of
LCD Main C.B.A.
-
flashes 4 times
every 5 seconds
flashes 4 times
every 5 seconds
IC2301(pin76) detects the Lamp Cover Unit condition
(open or close), then indicates the error when the
Lamp Cover Unit is open.
IC6001(pin85) detects the Duct FAN stop, then
indicates the error when the Duct FAN is stopped.
IC2301(pin74 and 75) detects open or short of the Temperature
Sensor (R2911) on Front Thermistor C.B.A., then indicates the
error when Temperature Sensor is open or shorted.
(The error is not detected for 1 minute after Lamp ON.)
IC2301(pin74 and 75) detects the temperature attached near
the Front FAN by the Temperature Sensor (R2911) on Front
Thermistor C.B.A., then indicates the error when the
temperature becomes more than 43 C (109 F).
(The error is not detected for 1 minute after Lamp ON.)
IC6001(pin86 and 87) detects open or short of the
Temperature Sensor (R2901) on Lamp Thermistor C.B.A.,
then indicates the error when Temperature Sensor is open or
shorted.
(The error is not detected for 4 minutes after Lamp ON.)
IC2301(pin74 and 75) detects the temperature attached near
the Lamp by the Temperature Sensor (R2901) on Lamp
Thermistor C.B.A., then indicates the error when the
temperature becomes more than 60 C (140 F).
(The error is not detected for 4 minutes after Lamp ON.)
IC2301(pin11) detects the error of LCD Power C.B.A.,
then indicates the error when the temperature fuse
(117 C)(243 F) in LCD Power C.B.A. is open.
IC2301(pin11) detects the error of LCD Power C.B.A. and Lamp,
then indicates the error when an inner malfunction of LCD Power
C.B.A. occurs, the Lamp voltage becomes more than 130V or
less than 30V, Lamp current becomes more than 5A, or the Lamp
is cracked.
IC2301(pin11) detects the error of the Lamp, then indicates the
error when the Lamp is short-circuit.
IC2301(pin48) detects +16V line voltage on LCD Main
C.B.A., then indicates the error when the voltage
becomes less than +13V.
IC2301(pin47) detects +14V line voltage on LCD Main
C.B.A., then indicates the error when the voltage
becomes less than +11V.
IC2301(pin45) detects +7V line voltage on LCD Main
C.B.A., then indicates the error when the voltage
becomes less than +5.7V.
IC2301(pin44) detects +3.3V line voltage on LCD Main
C.B.A., then indicates the error when the voltage
becomes less than +2.5V.
flashes 3 times
every 5 seconds
flashes 4 times
every 5 seconds
Abnormal Voltage
on 3.3 V line of
LCD Main C.B.A.
-
-
-
- flashes 5 times
every 5 seconds
Forced cooling
The failure of Lamp
light up
-
Temperature Sensor
short or open
-
-
Abnormal
Temperature
Duct Fan stop -
When accumulated operation time of the the Lamp reaches
5000 hours, OSD (replacing the Lamp) appears on the screen.
Note: The Lamp time is stored in EEPROM (IC2305).
When accumulated operation time of the Air Filter reaches 400
hours, OSD (cleaning the Air Filter) appears on the screen.
Note: The Filter time is stored in EEPROM (IC2305).
During forced cooling, this indication is indicated.
IC2301 (pin11) detects the failure of light up processing of
the Lamp, then the POWER LED is changed as follows.
1) POWER LED flashes green for 140 seconds (while turning on).
2) POWER LED flashes red for 60 seconds (while cooling).
3) POWER LED lights up red (standby).
Note: If the Lamp will not light after attempting turning on the
power 2 or 3 times, the Lamp, the LCD Power C.B.A. or the
LCD Main C.B.A. may be defective.
Error Symptom Problem Possible Solutio

Your hot surface igniter may be bad. It may be cracked which would prevent it from starting the burner flame.

Here's something that might also be useful. After you turn on the set, and get the regular red blinky lights, hold down the Device and Menu buttons together for about 5 seconds.
The Power light will start to flash in a two digit sequence.

For example, 3 flashes, then 7 flashes = 37.

Here are the error codes, and the corresponding problem:

12 = No error detected, check power supply.
32 = Lamp Cover is open.
33 = Air filter cover is open.
34 = Lamp abnormality
36 = Light Engine (DMD or Lamp Fan stopped)
37 = Exhaust or Lamp Ballast Fan stopped
38 = Lamp Temperature High
39 = DMD Temperature High
41 = Short is detected
44 = DVI cable between FMT and Engine disconnected

Here's something that might also be useful. After you turn on the set, and get the regular red blinky lights, hold down the Device and Menu buttons together for about 5 seconds.
The Power light will start to flash in a two digit sequence.

For example, 3 flashes, then 7 flashes = 37.

Here are the error codes, and the corresponding problem:

12 = No error detected, check power supply.
32 = Lamp Cover is open.
33 = Air filter cover is open.
34 = Lamp abnormality
36 = Light Engine (DMD or Lamp Fan stopped)
37 = Exhaust or Lamp Ballast Fan stopped
38 = Lamp Temperature High
39 = DMD Temperature High
41 = Short is detected
44 = DVI cable between FMT and Engine disconnected

Here's something that might also be useful. After you turn on the set, and get the regular red blinky lights, hold down the Device and Menu buttons together for about 5 seconds.
The Power light will start to flash in a two digit sequence.

For example, 3 flashes, then 7 flashes = 37.

Here are the error codes, and the corresponding problem:

12 = No error detected, check power supply.
32 = Lamp Cover is open.
33 = Air filter cover is open.
34 = Lamp abnormality
36 = Light Engine (DMD or Lamp Fan stopped)
37 = Exhaust or Lamp Ballast Fan stopped
38 = Lamp Temperature High
39 = DMD Temperature High
41 = Short is detected
44 = DVI cable between FMT and Engine disconnected