How to Troubleshoot an Iced-Up Heat Pump in the Winter


Ice on the heat pump is one of the most common HVAC problems in winter, along with outdoor tankless water heater freezing. A small amount of ice is no problem, but excessive amounts can damage your heat pump. In this blog, McLay shares a look at how to troubleshoot an iced up heat pump.

Why Do Heat Pumps Ice Up?

Heat pumps are equipped with a thermostat or sensor that detects ice buildup. A properly-operating heat pump should shift into cooling mode,  channel hot refrigerant through outside coils, and defrost the system. It’s important to note that this is different from snow. In fact, frost can form on the heat pump even at climates that don’t normally have below freezing temperatures.

Troubleshooting an Iced Up Heat Pump

If the heat pump is persistently icing despite running a defrost cycle, perform the following troubleshooting steps:

  1. Check the Refrigerant Levels — Low refrigerant levels mean your heat pump can’t efficiently defrost itself, allowing frost to continue building up. If this is the case, call an HVAC contractor/plumber like McLay.
  2. Malfunctioning Defrost Thermostat or Sensor — Your heat pump may not be automatically kicking into defrost more because it’s not detecting the ice buildup. Certain HVAC models have a thermostat “reset” procedure similar to regular thermostats. Consult your heat pump user guide, and follow the steps to reset the sensor or thermostat. Wait a few minutes and see if it switches to defrost. If not, call your HVAC technician.
  3. Check the Outdoor Fan Motors — Your heat pump needs the outdoor fan to perform its defrost cycle. If it stops working, you need to call for repairs.
  4. Replace Your Air Filters — Clogged air filters can cause the air pump to freeze, as it requires air flow to operate. Air filters are designed to be user-replaceable. When buying new air filters, make sure it’s the right size, otherwise you risk air leaks by forcing incorrectly-sized filters.

Call McLay for Your HVAC Needs

McLay is your leading provider of HVAC services, including installation of tankless water heater cold climate. Give us a call at (909) 392-2202 or fill out our contact form to schedule an appointment. We serve customers in La Verne and nearby areas.