Heat Pump Water Heater Not Heating: Filter, Room and Codes

By Ray Bennett · Updated 2 October 2026 · 6 min read · Checked against the makers’ own manuals

Heat Pump Water Heater Not Heating: Filter, Room and Codes

Short answer

A heat pump water heater takes its heat from the air around it, so the room matters as much as the machine. A.O. Smith's heat pump sits out when the air is below 45°F or above 120°F. A dirty air filter or a blocked condensate drain makes Rheem and GE models fall back to their elements, which cost more to run. Clean the filter, clear the drain, check the mode, then read the code.

A heat pump water heater, often sold as a hybrid, is an electric tank with a small heat pump on top. The heat pump pulls heat out of the air in the room and puts it into the water, and two ordinary elements stand by as backup.

That design explains most of its faults. The room, the air filter and the condensate drain matter as much as the parts inside. This page brings together what Rheem, A.O. Smith and GE say in their own manuals, as quoted on this site’s brand pages.

Before you start

What to carry: a torch, and a vacuum or mild detergent for the air filter. Twenty minutes.

Gas or electric? Electric, on a 240 volt circuit. The heat pump does most of the heating and the two elements are the backup.

Give it time after power comes on. A.O. Smith says its heater runs a system check at start up, typically about eight minutes, with scrolling dashes on the display.

Three things the makers are firm about. Never power it empty. GE says the elements are damaged if they run without water, and its warranty does not cover damage from an empty or part empty tank.

The high limit is for a technician. Rheem’s A200 means the high limit has tripped and the heater stays disabled. GE says a qualified technician should reset its manual reset limit and find out why it tripped.

Power and the filter. A.O. Smith says to turn its heater off at the breaker before cleaning the filter. GE’s filter lifts out from the top with the power left on. Follow your own model.

The room it sits in

The heat comes from the room's air. These are the makers' own limits and spacing.

Check 1

Check the room, not just the heater

Too cold or too hot. A.O. Smith’s HPO code means the air is below 45°F or above 120°F, or the tank averages 59°F or less. The heat pump sits out until conditions change, and A.O. Smith lists it as normal.

Too small a room. GE says a room smaller than 700 cubic feet, 10 by 10 by 7 feet, needs louvered doors or similar ventilation. It asks for 7 inches from the wall and 8 inches clear above the air filter.

Freezing. Rheem’s A130 means the unit is off and the air around it is below freezing. Select a mode to turn it back on.

Defrost. A.O. Smith’s ICE on the display is a defrost cycle, and normal.

Winter water. GE says colder water coming in takes longer to heat, which is normal, and the room around the heater feels cooler because that is where the heat comes from.

The air filter

Check 2Free, twenty minutes

Clean the filter

Rheem, T131. Set the mode to Electric or OFF, take the filter out, wash it with a mild detergent, let it dry, refit it and set your mode again.

A.O. Smith, SF. Power off first. Vacuum it in place, or slide it out by its two tabs and wash it with dish soap and water.

GE, F14 or the red filter light. Squeeze the two tabs on top and lift it out. Vacuum, wipe or rinse it, let it dry, refit it, then press and hold FILTER to reset.

Why it matters. GE says a filter that gets too dirty switches the heater to its electric mode, and the savings are lost. It adds that a filter alarm returning within days may mean a refrigerant leak.

The condensate drain

What a fault does to the heating. Several leave you hot water from the elements, at a higher cost, until they are fixed.

Check 3Free, or a pump

Clear the drain

Rheem, A108. Check the condensate line is clear and the pan is not full, and if water is sitting there, find the blockage and clear it.

A.O. Smith, EoF. If a condensate pump is fitted, check it is plugged in and powered, including its breaker and any GFCI. Then check its outlet tube, and that the heater stands level so the pan drains: a condensate pump not working.

GE, F20. The drain is clogged and the heat pump has stopped. Clear the drain lines. GE says the elements keep making hot water until it runs again.

The mode, and running out

Check 4

Match the mode to the house

GE’s modes. Heat Pump is the cheapest to run and the slowest. Hybrid is the factory setting. High Demand, or Boost, brings the elements in sooner for a household that uses more hot water.

It cannot keep up. Rheem’s T132 says to check for open taps and leaks, and that if there are none the heater may be too small for the house.

A flashing green light. GE says that in Hybrid and High Demand modes, the Electric light flashes while the elements heat, which is normal.

The set temperature. GE suggests raising it in winter: what temperature to set.

When it will not heat at all

Check 5Free to a technician

Rule out the tank and the power

The tank is not full. Rheem’s A008, A.O. Smith’s Edr and GE’s F11. Fill it and purge the air by running the hot taps. A.O. Smith says open every hot tap at full stream for three minutes.

The wrong voltage. GE’s F12, shown as bAd linE, means it is not getting its 240 volts. A.O. Smith’s EPL points at loose electrical connections, a job for an electrician.

The compressor. Rheem says it does not repair sealed system parts: a failed or leaking compressor means a new unit.

An element. The backup elements are tested and replaced like any electric tank’s: testing an element.

The same fault, by maker

Fault	Rheem	A.O. Smith	GE GeoSpring
Air filter dirty	T131	SF	F14, red filter light
Condensate drain blocked	A108	EoF	F20
Tank not full	A008	Edr	F11
Air too cold	A130, freezing	HPO, below 45°F	Not listed
High limit tripped	A200	Not listed	The TCO, a technician’s reset

The full lists are on the brand pages: Rheem, A.O. Smith and GE GeoSpring.

Questions people ask

Why is my heat pump water heater not heating?

Check the room first: A.O. Smith’s heat pump stops below 45°F or above 120°F air. Then the air filter, the condensate drain, the mode, and any code on the display.

Why is my hybrid water heater using so much electricity?

It is probably running on its elements. A dirty filter, a blocked condensate drain or a compressor fault makes the Rheem and GE models fall back to the elements.

How often should I clean the air filter?

When the heater asks for it: Rheem’s T131, A.O. Smith’s SF or GE’s filter light. GE says a filter alarm that returns within days may mean a refrigerant leak.

Can a heat pump water heater go in a small closet?

GE says a room under 700 cubic feet needs louvered doors or similar ventilation, because the heat pump draws its heat from the room air.

Why is the room around my water heater cold?

That is how it works. GE says the heat in the water comes from the air around it, so a cooler room is normal.

Should I use Heat Pump or Hybrid mode?

GE says Heat Pump mode costs least and heats slowest. Hybrid is the factory setting. High Demand brings the elements in sooner for heavy use.

Sources: The makers' own documents, as cited on this site's brand pages: Rheem use and care manual AP23657, the A.O. Smith hybrid service handbook (HPTU, FHPT, SHPT) and the GE GeoSpring owner's manual 49-50300-2