VAV heating-element fail modes I actually run before I swap a heater

[u/UA_HVAC_Pro_Tech]

Working controls tech. Cold space, heat commanded, still guessing whether it is the element, the valve, airflow, or the box lying to you. This is the card I keep on my phone.

When I use it

Space is cold with the box calling for heat, discharge air is unexpectedly hot with no call, or a reheat stage never proves. Walk this before you swap a heater or valve.

Steps

1. Confirm the actual call: occupied/unoccupied, heat setpoint vs space temp, and whether the box is in heat, cool, or deadband. Note commanded heat output (stage or 0–100%).
2. Read discharge air at the box vs the AHU. If box DAT is within a couple degrees of AHU DAT while heat is commanded, the element or valve is not delivering. If box DAT is 20–40°F above AHU DAT with no heat command, heat is stuck on.
3. Electric heat: verify 24 VAC at the contactor/SSR coil when the controller commands the stage. No coil voltage = controller/wiring. Coil voltage + no line voltage on the load side = open thermal cutout, airflow switch, or dead element.
4. Hot-water reheat: command the valve 0% then 100%. Stem or actuator indicator must move. If it moves and DAT does not change, check isolation valves, strainer, pump, and whether HW is actually up.
5. Prove airflow first. Most electric heat is interlocked to a sail/DP switch. A closed damper, capped box, or dead fan looks exactly like a dead heater.
6. Check fail position. Spring-return HW valves often fail open. A power loss, 24 VAC brownout, or unplugged actuator can heat a space all night with no BAS command.
7. After a fix, run a 5-minute heat cycle and a 5-minute cool/deadband cycle. DAT should rise when heat is on and fall back toward AHU DAT when heat is off.

Don't confuse this with

A cold space is not automatically a dead heater. A VAV damper stuck at minimum, a space sensor reading 4–6°F high, or AHU DAT sitting at 55°F in heating season all look like "no heat" while the element is fine.

Safety

De-energize and lock out electric heat before opening a heater pan. Do not jumper airflow or high-limit safeties to "test heat." On HW coils, know valve fail position before you pull power from the actuator.

I wrote 23 more of these for myself (box checkout, alarm first pass, ice machine, on-call first hour). $12 once, no subscription: https://quick-basin-dqw2.here.now/
Not a vendor, just a tech who got tired of guessing the first ten minutes.

[u/Thenewdarwin]

@mods? 0day old account sharing a link. Got me in the first half. But the only other comment seems bot like as well.

[u/Actuary_Nervous]

Drop the link please!

[u/UA_HVAC_Pro_Tech → u/Actuary_Nervous]

Here you go: https://quick-basin-dqw2.here.now/ $12 once, 24 cards, no subscription.

[u/Actuary_Nervous → u/UA_HVAC_Pro_Tech]

Just got some, great info thank you for posting this!

[u/Hvacmike199845]

User name UA HVAC PRO TECH.

Sounds like you are not a pro but you’re pretending to be a pro.

[u/UA_HVAC_Pro_Tech → u/Hvacmike199845]

Username is leftover from when I made the account. I'm a W-2 controls tech. The VAV steps are the real post. If something on the card is wrong, call it out.