Got a problem which had me going crazy but I think I’m getting closer to resolving it. Basically my carrier furnace (which has been running for many years) started throwing code 33’s and basically not keeping the house warm enough last week. I couldn’t find anything wrong with the airflow or rollout or anything.

Then I remembered I had my gas meter/regulator replaced with a larger one 2 months ago for my generac generator project. (You may recall my previous posts here concerning that). When the gas company guy was out doing that, he was asking what I was up to and upon hearing about the generator, he said he was setting the regulator for 7.5” WC. The generac calls for 5-7” but he said something about the pressure drop.

No adjustments were made at the time to the existing furnace and water heater in my home.

Now, I believe my furnace may be overfired and throwing code 33’s because the master high limit is tripping. I ordered a “yellow jacket” water manometer and it’s arriving tomorrow.

I have the following questions:

1. Should I drop the main regulator (at meter) to 7” WC? The generac can operate from 5-7” so I would imagine this would be fine.

2. The carrier furnace calls for 3.5” WC at the manifold. When setting this, do I need the generac and water heater running at full consumption? Or should I isolate to the furnace when making the adjustment?

3. I don’t see any adjustment screw/manometer port on the GE (AO Smith) water heater. Do water heaters even need manifold adjustments?

4. I don’t see anything about manifold pressure adjustments in the Generac install manual. Am I missing something here or does it autosense the pressure or something like that?

Thanks for your advise!

lots of videos on you tube about adjusting gas pressure to a furnace.
the majority of gas valves are honeywell and even if yours isn't, they all have a pressure port for attaching the gauge and also have a screw for adjusting the pressure.
here is a generic video about setting pressure..
[www.youtube.com]

Thanks Packy, but can you comment on my other questions such as the water heater? Thanks!

Many gas valves, especially water heaters, have an internal pressure regulator.

[waterheatertimer.org]

Great link, I have the “white Rodgers mechanical” valve, so there’s a test port hidden under the bottom but no adjustment. Looking forward to playing around with the yellow jacket tomorrow! Learning something new.