Bunn Heating Time Too Long

What does Bunn Heating Time Too Long mean?

On AXIOM digital brewers, the control board tracks how long the tank heaters run to bring the water up to brewing temperature. If the water does not reach the ready temperature within the allowed time, the display reports Heating Time Too Long and shuts the brewer down. This protects the brewer when a heater or the temperature sensing path is not working as expected.

Symptoms

• Display reads "Heating Time Too Long"
• Water does not heat to the proper temperature
• Brewer never reaches ready
• Brew is locked out because tank temperature is low

Common causes

• Tank heater failure
• Control board failure
• Thermistor (temperature sensor) failure

Diagnostic steps

1. 01

   Let the tank temperature stabilize first

   Do not take temperature readings before the display reads ready. Tank temperature must be stabilized before any heating fault is judged.

2. 02

   Test the tank heater

   Check the tank heater for failure. Replace or repair it as needed if it is not heating the tank water.

3. 03

   Check the temperature probe / thermistor

   A failed thermistor can make the board think the tank is not heating. Check and replace the temperature probe if it reads out of range.

4. 04

   Check the control board

   If the heater and thermistor are good, the control board may have failed. Replace or repair as needed and re-test the heat-up cycle.

When to call a professional

Tank heaters carry full line voltage and the brewer is heated at all times, so the manual restricts testing and repair to qualified service personnel. Diagnosing whether the heater, thermistor, or control board is at fault requires live electrical testing where shorting terminals can destroy the board. Have a Bunn Authorized Service Representative perform these heater and board tests rather than working on energized components yourself.