How to diagnose an intermittent equipment problem that only happened once
Intermittent equipment issues that disappear by the time a technician arrives are nearly impossible to diagnose because normal tests show nothing wrong. This leaves people unable to catch the problem before it worsens or get repair help for a fault that refuses to replicate on demand.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
How to diagnose an intermittent equipment problem that only happened once
- 1shutting the unit off manually and turning it back onDid this help you?
- 2waiting for the issue to return before attempting further diagnosticsDid this help you?
- 3monitoring suspect componentsDid this help you?
- 4Recording videos of the issue to show techniciansDid this help you?
- 5Turning off the circuit breaker for an hour to reset itDid this help you?
- 6Getting a second opinion from another companyDid this help you?
- 7Installing hard-start kitsDid this help you?
- 8Bringing in alternative subcontractors to troubleshootDid this help you?
- 9Racking up repair costs while waiting for answersDid this help you?
- 10Calling HVAC technicians for recurring repairsDid this help you?
- 11Considering replacing the unit entirelyDid this help you?
- 12Considering switching to a dedicated AC and baseboard heatersDid this help you?
- 13Considering learning HVAC repair independentlyDid this help you?
- 14turning on and off the breakers inside of the furnace housing to reset itDid this help you?
- 15Accepting out-of-pocket labor costs when equipment failures happen just outside the warranty windowDid this help you?
- 16Conducting independent research to question technician diagnosesDid this help you?
- 17Adjusting the air filter while the noise is happening to see if it changes the sound.Did this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I've had HVAC guys out multiple times, but by the time they get out to my house, the unit is running normally and they say it cools at normal levels. They said they can't really diagnose it since it's working fine while they are there.”source ↗
“Towards the end of May this year, we started having issues with the blower inside not wanting to kick on.”source ↗
“Right away, in 2025 Spring we started seeing the various A/C breakers tripping randomly when air conditioning was being used.”source ↗
“This year, what's worse is that the blower motors are starting to go bad. It started with one blower motor a month or so ago and we just had a second one go bad.”source ↗
“So, we are continuing to rack up repair costs without anyone having any idea of what might actually be going on.”source ↗
“Around every 6 months, generally right when it gets really cold or hot, the thing shuts down and the light flashes. I’m left calling hvac to repair, but it’s never once gone smoothly.”source ↗
“I’ve put around 7k$ + into this unit so far. Is this amount of maintenance normal for daikin or all mini splits?”source ↗
“The furnace has been vibrating and making an ungodly amount of noise 5 nights of the last 6.”source ↗
“The HVAC company has heen out twice and have no idea whats wrong, as they cant recreate it and the unit is passing diagnostics.”source ↗
“I recently experienced a problem with my electric heat pump where the house temperature exceeded the thermostat cooling setting by 3 degrees.”source ↗
“I am hoping to that if the problem reoccurred to catch it before it creates a more severe problem.”source ↗
“trying to troubleshoot a problem that happened once about a week ago is like trying to find a needle in a haystack.”source ↗
“This week the compressor blew. "Catastrophically" according to the technician.”source ↗
“I brained it some and did some research and I was wondering what the likelihood is that it blew because of an overcharged system (a fault of their's during the previous service call) and not bad factory windings or something on the motor.”source ↗
Where this came up
People with this problem also raised
- 17Why are equipment service bills so expensive for minor fixes?
- 76HubSpot is down and timing out right now
- 2Why is my combi boiler so unreliable?
- 5Why does touching my breaker panel turn my electric dryer back on?
- 6Why does my electrical outlet only work sometimes?
- 2Why does my tankless water heater keep short cycling?