Question about Mr. Heater MHU45LP

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Blower starts but ignitor will not fire. 3 flash fault on control board which the manual says is a pressure switch failure. worked fine when i shut it down this spring.

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Jump out the switch to test it. It could have a blockage in the line or it could be bad. Check the air intake and exhaust venting, there could be a blockage it it as well.

Posted on Nov 15, 2009

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The unit cycles through all levels and then displays Ignition failure, code B2. I replaced the flame sensor, the ignitor, and there is natural gas at the gas valve.


Sequence of operation for most Gas fired furnaces...
Demand for heat from t-stat
Control board demands combustion chamber purge
(IDM /induced draft motor if it has one)
Control board tests all safeties (this is usually via
the IDM wiring.)
Control board sends 24v to PV at the gas valve igniting
the pilot OR control board sends voltage to the
ignitor as in yours.
Control board sends 24v to MV at the gas valve.
Control board allows time for heat exchanger to warm
then calls for blower operation.

Your sequence of operation? Won't be the flame sensor unless ignion has been achieved. If the ignitor is working/glowing red? Is the IDM working? Make & model#?

May 26, 2015 | Heating & Cooling

1 Answer

My Bryant Gas furnace model number is 373LAV036095 the pilot light won't light. Gives us indication that the pressure value is stuck??? Sends into lockout mode. Where is the pressure value located in the...


This is a down flow unit. There is no pressure valve on this unit. Here is all the parts on this unit.
1. Manual - reset, when used.
2. Blower and blower motor
3. Relief box also known as a exhaust flue.
4. Gas valve control knob or electric switch, ON/OFF
5. Gas Valve
6. Gas burner
7. Ratting plate
8. Blower door safety switch
9. Blocked vent safeguard tube and switch
10. Gas Manifold
11. Manual limit switch (2)
12.Hot surface ignitor
13. Flame sensor
14. Inducer blower motor
15. Control board with relays and transformer.
That is all the parts. The first thing the heater gets a call from the thermostat to the control board marked W. The board sends 24v to the inducer fan relay which makes and causes the inducer fan to come on now there is a small tube that runs from the inducer fan box to a switch when the switch makes it sends power to the board which proves you have cleared the exhaust flue then the flat surface ignitor starts to glow and then gas valve opens and fires. now if this tube is stopped up the heater will not fire and will lock the unit out. Also if the flue is stopped up with trash it will do the same thing. If you are not familiar with gas heating units you should call a service company out and check out the system there is a lot of things that need to be checked out every heating season as to keep you and your family safe.

Mar 02, 2015 | Heating & Cooling

1 Answer

I tried turning it back on got code 33 for about 3 minutes then went back to 13. Now the filter was very dirty, and I have to be honest it was very dirty. The instrutions say to wait for 3 hours. If I...


this being a gas unit should either be plugged in or have a power switch near the furnace if not go turn the breaker off for about ten seconds the heat breaker or furnace however it is labled...this will reset the control board and allow it to start over...your correct if it trys to lite and after 3 times it will go into a 3 hour lockout but you can manually reset it by killing the power to unit... allow it to start up again... some units once repowered will start off with the blower running for 90-120 seconds as a power up stage and then after that is over the small inducer draft motor or combustion chamber motor will start it pulls a vacum on the negative pressure switch ( round device with a hose connected to it) after the pressure switch closes it should send power to you rignitor device ( not sure if this model has a ignitor/glow plug or if it is spark igniton if the ignitor or spark igniton doesnt start then you can test to see if voltage is being sent to the ignitor by unplugging and put you meter in it should read 120 volts if you have power but not glow or spark its bad. next aftr it glows then gas valve will open and it will attempt to fire... code 33 is a firing issue i believe the installer should have put the sticker that has the fault codes on it to tell you what it is...if not shame on them... after it fires off there is a flame sensor rod inside the direct path of the flame that senses flame and tells the board to keep gas coming if it fires but goes off that is dirty ann needs lightly sanded dont get wild with it... ok thats the operation if the blower never shuts off or the unit never trys to start up at all you just have a blower one of your limit devices is open..try the small limits around the burner most have a button to push and reset...if all good then sometimes on the blower there is a limit check it for contuinity with the wires off it should beep or read also there is a main limit that is usually squre and about 2 inches in size remove wires from it and check it should be closed if you dont have meter you can temporarily tape wires together they are low voltage and ill not hurt you but if you touch metal while power going to unit can short out board or transformer so while testing of removing wires unplug or turn unit off.... good luck to you...

Feb 18, 2011 | Heating & Cooling

2 Answers

I have a Arcoaire Gas Furnace (Model# GNJ100N12A1), that will not fire up. It has a White Rogers Digital Stat. First the Stat seems to be faulty, since it reads 70plus in a house that has a temp of 30...


Sounds like a faulty board. shut the power to the furnace off for a minute then turn it back on. Make a call for heat at the thermostat. The inducer should start and close contacts on a pressure switch . Once pressure switch closes the hot surface ignitor should glow red. Then the gas valve will open when the gas valve opens you should get fire till the stat is satisfied. If your concerned it is the jump out r to w on the board this will eliminate the stat. If you to reset the rollout switchs 3 timesyou're getting flame rollout and you either have a cracked heat exchanger or blockage in the exhaust piping or a bad inducer motor. Keep me posted with what you find!

Dec 15, 2010 | Heating & Cooling

2 Answers

Will not light blower comes on i here it click but no flame i get a if code


Using a manometer, check the manifold gas pressure during start up. Does it go up to about 3" WC? If so, bleed the air out of the line until you get a strong smell of gas and try again.

If you are not getting any gas pressure you will need to check the power coming to the gas valve. Are you getting 24V at any point during the start up process? If so, the valve is bad and needs to be replaced. If not you will need a new control board.

John

Oct 18, 2010 | Hayward H400FDN Low NOx Natural Gas Pool...

1 Answer

What are the carrier 8000ts led error codes?


They are listed inside the front panel of the main unit.

LED CODE

EACH OF THE FOLLOWING STATUS CODES IS A TWO DIGIT NUMBER WITH THE FIRST

DIGIT DETERMINED BY THE NUMBER OF SHORT FLASHES AND THE SECOND DIGIT BY

THE NUMBER OF LONG FLASHES.

STATUS

11 NO PREVIOUS CODE - Stored status code is erased automatically after 72

hours. On RED LED boards stored status codes can also be erased when power

(115 VAC or 24 VAC) to control is interrupted.

12 BLOWER ON AFTER POWER UP (115 VAC or 24 VAC) -Blower runs for 90

seconds, if unit is powered up during a call for heat (R-W closed) or R-W opens

during blower on-delay.

13 LIMIT CIRCUIT LOCKOUT - Lockout occurs if the limit or flame rollout switch is

open longer than 3 minutes.

- Control will auto reset after three hours. - Refer to #33.

14 IGNITION LOCKOUT - Control will auto-reset after three hours. Refer to #34.

21 GAS HEATING LOCKOUT - Control will NOT auto reset.

Check for: - Mis-wired gas valve -Defective control (valve relay)

22 ABNORMAL FLAME-PROVING SIGNAL - Flame is proved while gas valve is

de-energized. Inducer will run until fault is cleared. Check for:

- Leaky gas valve - Stuck-open gas valve

23 PRESSURE SWITCH DID NOT OPEN Check for:

- Obstructed pressure tubing. - Pressure switch stuck closed.

24 SECONDARY VOLTAGE FUSE IS OPEN Check for:

- Short circuit in secondary voltage (24VAC) wiring.

31 PRESSURE SWITCH DID NOT CLOSE OR REOPENED - If open longer than

five minutes, inducer shuts off for 15 minutes before retry. Check for:

- Excessive wind - Proper vent sizing - Defective inducer motor

- Low inducer voltage (115VAC) - Defective pressure switch

- Inadequate combustion air supply - Restricted vent

- Disconnected or obstructed pressure tubing

- Low inlet gas pressure (if LGPS used)

If it opens during blower on-delay period, blower will come on for the selected

blower off-delay.

33 LIMIT CIRCUIT FAULT - Indicates a limit, or flame rollout is open. Blower will

run for 4 minutes or until open switch remakes whichever is longer. If open

longer than 3 minutes, code changes to lockout #13. If open less than 3 minutes

status code #33 continues to flash until blower shuts off. Flame rollout switch

requires manual reset. Check for: - Restricted vent

- Proper vent sizing - Loose blower wheel - Excessive wind

- Dirty filter or restricted duct system.

- Defective blower motor or capacitor. - Defective switch or connections.

- Inadequate combustion air supply (Flame Roll-out Switch open).

34 IGNITION PROVING FAILURE - Control will try three more times before lockout

#14 occurs. If flame signal lost during blower on-delay period, blower will come

on for the selected blower off-delay. Check for: - Control ground continuity

- Flame sensor must not be grounded

- Oxide buildup on flame sensor (clean with fine steel wool).

- Proper flame sense microamps (.5 microamps D.C. min., 4.0 - 6.0 nominal).

- Gas valve defective or gas valve turned off - Manual valve shut-off

- Defective Hot Surface Ignitor

- Low inlet gas pressure

- Inadequate flame carryover or rough ignition

- Green/Yellow wire MUST be connected to furnace sheet metal

45 CONTROL CIRCUITRY LOCKOUT Auto-reset after one hour lockout due to;

- Gas valve relay stuck open - Flame sense circuit failure

- Software check error

Reset power to clear lockout. Replace control if status code repeats.

If status code recall is needed, briefly remove then reconnect one main limit wire to display

stored status code. On RED LED boards do not remove power or blower door before initiating

status code recall. After one status code recall is completed component test will occur.


Thanks for Choosing FixYa.


Kelly

Oct 05, 2010 | Heating & Cooling

2 Answers

The heat turns off after 3 seconds of flame.


There is a flame sensor failure.

Here is the ignition sequence for a furnace. This will help you understand what is happening/not happening.

Thermostat2.gif calls for heat.

draft inducer motor (DIM) starts drawing draft through heat exchanger.

Pressure switch detects proper operation of DIM, and sends signal to board to begin ignition.
(it detects negative pressure)

Ignitor starts ignition attempt and gas valve sends gas to burners.

Upon ignition, flame sensor detects flame and sends signal to board stopping ignition sequence and continuing gas flow for heat mode operation until thermostat is satisfied.

During this sequence the blower motor is brought on, and by using a series of temperature limit switches, the system assures that the unit is operating properly.
(If the blower is not operating, or the airflow is inadequate, the heat exchanger will overheat and trip one or more temp limit switches.)

There is also a "rollout" switch that detects improper flame pattern "rolling out" into the controls compartment.

Now, to apply that to your situation.

If the flame sensor does not sense flame, it shuts down the furnace to prevent a dangerouse gas build up.

With most modern glow coil ignition systems you have one of two failures.

1) the flame sensor is bad and needs to be replaced.

2) the control board is not proccesing the signal from the flame sensor and shuts the system down. In that case the board would need to be replaced.

There is a possibility that a temperature limit or roll out switch is breaking the curcuit, but that would be quite unusual to happen consistantly at three seconds.

Unless you have the ability and tools to test the snesor and board, the next step would be to replace the sensor first, and then the board if that does not fix it.

Oct 03, 2009 | Maytag Neptune MDG5500AW Gas Dryer

2 Answers

Blower turns on when stat calls for heat but manifold is not being ignited (do not hear gas valve even trying to release gas). No spark either. Could it be insufficent gas pressure?


Here is the ignition sequence for a spark ignited furnace. This will help you understand what is happening/not happening.

Thermostat calls for heat.

draft inducer motor (DIM) starts drawing draft through heat exchanger.

Pressure switch detects proper operation of DIM, and sends signal to board to begin ignition.
(it detects negative pressure)

Ignitor starts ignition attempt and gas valve sends gas to burners.

Upon ignition, flame sensor detects flame and sends signal to board stopping ignition sequence and continuing gas flow for heat mode operation until thermostat is satisfied.

During this sequence the blower motor is brought on, and by using a series of temperature limit switches, the system assures that the unit is operating properly.
(If the blower is not operating, or the airflow is inadequate, the heat exchanger will overheat and trip one or more temp limit switches.)

There is also a "rollout" switch that detects improper flame pattern "rolling out" into the controls compartment.

Now, to apply that to your situation.

If you have no spark, than the failure is happening before the gas is supposed to be flowing.

That usually means a failure at the D.I.M. Typical causes for that are a clogged flue pipe/vent, damaged/deteriorated fan blades, bad fan, or bad pressure switch.

If one of the temp limit switches or rollout switches have tripped, it will simply shut off the system.
(Some units will turn on the blower motor and shut down everything else.)

You can try resetting the unit by disconnecting power for 1 minute, and attempting a restart.

First look for any flashing LED lights. If you see any locate the wiring schematic (usually on the inside of the front panel) and look for the flash codes.

If the reset does not solve the problem, let me know what flash code you are getting, and/or let me know exactly what you see the furnace doing, in detail, after the restart.

Oct 03, 2009 | Weather King 12AJA4801AH Air Conditioner

1 Answer

Fault code 6 flashes


Well, as you know the blower comes on because there is a control voltage (24V) failure.

I would trace out all the 24V wiring with the schematic to make sure someone didn't cross up a wire.

Then ohm out each component to make sure there is not a bad part in the 24V cycle.

Make sure you have voltage going to the ignitor from the board.

Obviosly the draft inducer motor is working, so thats not the issue. However the pressure switch could be having problems, thus interupting the 24 V cycle.

If you have power to the ignitor, and no ignitor op, then the board is OK. If the board is not sending power to the ignitor, after recieving signal from the pressure switch, then the board is bad.

Make sure the pressure switch is closing, and sending signal to the board.

Jan 19, 2009 | Heating & Cooling

5 Answers

Goodman furnace I think


Ok, a flashing 3 on a Goodman control board usually means that the pressure switch is tripping. A few things will cause this. One being a restriction in the exhaust or combustion air inlet. The second could indicate a faulty inducer blower motor and the third would be a blocked or bad pressure switch.
 
With the front cover off and door switch taped down, Have a helper turn the thermostat up to 75. You will be watching the circuit board for flashing lights and in a few seconds the inducer motor (the small fan hooked to the exhaust) will start. If this does not happen, we either have a bad circuit board or blower motor. If the fan starts rotating, inspect the hoses going to the small circular pressure switch. Sometimes they may get either water or debris in the hose and not allow the switch to sense pressure. If the hoses look OK, the igniter will glow an orange color and you will see this if you look thru the small viewing port. IF no glow, you could have a bad pressure switch, a bad ignition relay (found on the circuit board) or a bad igniter. OK so if the igniter glows, a few seconds later the gas valve should click open and send gas to the burners. The orange will turn to blue. If this does not happen, you have either a bad gas valve or bad circuit board. Finally if you get flame but it will not stay lit more than a few seconds, you may have a restriction in the burner gas train, a bad gas valve, a dirty or bad flame sensor or not enough gas pressure.
 
Knowing the sequence of operation will give you the needed information to talk with a service technician and cut down on diagnostic costs.
 
Try looking on the back of the furnace access panel for both model number and a diagnostic schematic. This will confirm what the flashing 3 code means for your unit.
 
Sorry, without knowing the model number, this is the best I can do for you. Good Luck!

Oct 28, 2007 | Goodman GMS90703BXA Heater

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