Question about Ruud UBHC Air Conditioner

1 Answer

Ruud achiever 90 plus wouldn't start

I had my furnace fail to start for me this morning, the fault code was 4 blinks and that means "pressure switch closed" according to the wiring diagram... but I fixed it by wiggling the pressure switch and it "clicked".  How do I keep this from happening again?  If you can help I can email Pix and a more detailed description.

Posted by on


1 Answer

  • Level 1:

    An expert who has achieved level 1.


    An expert that got 5 achievements.


    An expert whose answer got voted for 20 times.


    An expert who has written 20 answers of more than 400 characters.

  • Contributor
  • 54 Answers

Thanks for the carefull description of the fault, The vent system is designed so that if a leak occurs fresh air from the living space will be pulled into the vent rather than dangerous combustion gases pushed out to insure this there is a carefully calibrated -pressure switch that will not allow the unit to fire unless a negative pressure on the vent is proven this can be prevented by many things, here are a a few :a sticky micro switch, a leaking hose from the vent to the pressure sensor, cold stacking in the flu(either a down draft or extremely cold air in vent that restricts warm combustion air from being pushed out), a problem with the power exhaust fan(debris has gotten in the housing preventing an easy start), i usually find the cause to either be a bad pressure sensor hose or debris in ths exhaust fan housing either blocking blade movement or obstructing the pressure sensor hose port.
To clear the fault turn of the breaker to the unit then restart the unit and fallow the sequence of operation to see where the fault occurs the fan should come on first then the exhaust blower should come on when negative pressure is achieved it start the lighting sequence if the lighting sequence doesn't start and you get the same fault take the neg pressure hose loose from the exhaust fan housing and start the sequence again while pulling a slight negative pressure on the pressure sensor with a hand held pump continue this process until you find the fault.

Posted on Mar 11, 2008


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

A 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
The service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
Good luck!

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Ruud achiever 90 plus gas furnace flame goes out after few seconds

This could be water in the hoses that connect to the pressure switch , they should just pull off and blow then out also blow out the pressure switch , this sound like a moisture problem with all the bad weather you h, check air filter is not blocked .

Feb 12, 2013 | Heating & Cooling

1 Answer

RUUD Achiever 90 plus 2-blinks

read the back of the furnace panel, it will tell you what the blinks mean

Dec 15, 2012 | Heating & Cooling

1 Answer

I have a Ruud Achiever 90 Plus furnace that will not ignite and is showing a 'soft lockout' code on the LED panel. I've tried restting the furnace as per the manual and still no results. Am I missing...

Hello. a soft lockout typically happens when

1) the flame sensor is not detecting the flame
2) pressure switch fails to close

Since your burners are not igniting I would check the pressure switch, make sure there is no obstruction in the flue pipe, the hose going from inducer to pressure switch is not kinked, loose, obstructed, or have water in it. If that all checks out good then your pressure switch is bad and must be replaced. If you need any further assisatnce let me know

Mar 09, 2011 | Heating & Cooling

1 Answer

Ruud achiever 90 plus furnace will not start with door on.

I would try to check your return air first, making sure there is no blockage and that your air filters are clean. It almost sounds like when you take the cover off, you are pulling enough air into the system for it to run, but as soon as you close it off, it's not getting enough air flow, therefore, tripping a limit switch inside the furnace. Most furnaces will also have the codes for the flashing lights and what they mean on the inside of the door covers.

Feb 02, 2010 | LG LW1200ER Air Conditioner

1 Answer

Ruud achiever 90 plus won`t start

Check the data information on the unit there should be a troubleshooting guide that tells you what the two lights blinking once means. hope this helps.good luck. normally found with schematic

Feb 05, 2009 | Ruud UBHC Air Conditioner

1 Answer

Ruud achiever 90 plus blower not working

does the furnace ignite?? your system may not have been lighting and has gone into ignition lockout count the codes of the led lights then remove panel led diagnostic codes are listed there.
if led codes indicate no problem verify capacitor is good and that mtr is getting 115 volts.

Sep 15, 2008 | Ruud UBHC Air Conditioner

5 Answers

Ruud Achiever 90 Plus wont start

4 blinks is "pressure switch closed" there are 2 in the system according to the wiring diagram one for the vent system  and one for the drain system ... I just wiggled them and heard one "click" the fault light quit blinking and when I pushed the safety switch back in the furnace fired right up.  That being said is there a good website for learning how to maintain your own furnace?  I'll call a pro if I have to, but shoot I can fix a jet engine... this shouldn't be much worse.
Thanks  dan

Jan 19, 2008 | Ruud UBHC Air Conditioner

Not finding what you are looking for?
Ruud UBHC Air Conditioner Logo

513 people viewed this question

Ask a Question

Usually answered in minutes!

Top Ruud Heating & Cooling Experts

Bill Long

Level 3 Expert

588 Answers

Tim Whalen

Level 3 Expert

3074 Answers

Dennis Boxerman

Level 3 Expert

1238 Answers

Are you a Ruud Heating and Cooling Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides