Comeback: furnace quits again

2019 travel trailer, ducted furnace. 30A shore

Customer says: You fixed the furnace last week. It quit again last night.

Last week's RO says: Furnace no ignition. Replaced control board. Operates normally. No readings written down.

Tests you can run

• Read last week's repair order
• Run the furnace now
• Wiggle test: meter on the board's 12V input, flex the harness a section at a time while it runs
• Pull the 12V spade connector at the furnace and look
• Leave a recording meter on the board's input overnight
• Gas pressure at the furnace during a run
• Sail switch with the blower running
• Replace the control board again

Repair options

The lesson behind this case

• Chasing intermittent problems
• The repair note

Keep going on furnaces

Learn it

• Furnace sequence
• LP system basics

Prove it

• Furnace blows cold
• Furnace sparks but never lights
• Furnace keeps shutting off, fan keeps blowing
• Thermostat clicks, furnace does nothing

See it in 3D

• Furnace 3D wiring model

Codes and specs

• Furnace: suburban + atwood/dometic (12v dsi)
• Hydronic heat: aqua-hot 450-de/dm

On the job

• Furnace
• Thermostat