This article is a troubleshooting heat pumps guide of the most popular models in North America for residential use, and from the manufacturers; AO Smith, Bradford White, Rheem, State, Kenmore, Reliance, American and other. The article deals with the main causes of the heat pump failure, symptoms, error codes and recommendations for an easy and safe repair.
It will be assumed that the heat pump was properly installed - per codes and manufacturer’s instructions. This includes properly selected room for the unit, electrical and water connections in place, installed air filter and condensate lines and tank filled with water.
The first step in diagnosis the problem and troubleshooting is to simply disconnect the unit for some time ( the time depends on the model), resume the power and determine if the error code is still present or not. If, after the resumed power, the error code is still ON, read further, and find the instructions on how to repair the unit.
In order to fix the problem fast and correctly it is good to know what the main parts of the heat pumps are and what’s consider as the normal operation.
For example; normal operating temperature of the heat pump is between 32 F and 150 F. All the heat pumps are equipped with the electric fan and the compressor, so it is normal to hear some noise, but not the abnormal sound. Some noise can also be heard during the metal part contraction (cooling) and expansion (heating).
For any problem related to the heat pump, recommendation is to call the technician, but if you are planning to troubleshoot, here are the most common problems with the instructions:
The surrounding air gets colder
No hot water / not enough supply of hot water to the shower/faucets
Water is too hot
TPR valve – noise and dripping
Rotten egg odor
A problem with the compressor
High operating costs
When the heat pump operates, the room air gets cooler… and that is normal. For the correct and efficient operation, the installation room should have a recommended size, proper clearances around the unit and vented correctly, so enough air is coming in and through the heat pump. The heat pump uses the warm air for water heating, while it releases the air which is colder than the surrounding. One of the ways to provide more air for normal operation is to install the louvered door, so air can get in from the adjacent room.
If the water is dripping down the outside of the water heater, the water connections should be inspected for any loose joints or the heater’s condensate drain as it might be dirty and clogged. For example, if the water leaks around the elements (gasket or threads) re-seal or replace the gasket. The best solution for these problems is the regular maintenance and unit cleaning. During the water heater installation, a suitable drain pan is installed under the unit, to catch condensation or water leak, and from there piped to the appropriate drain. Since the leaking water can damage the property it is recommended to install the automatic leak detector with the shutoff device.
This is what needs to be checked and fixed:
The temperature of water on the thermostat might be set too low – increase if it is needed. The unit is in a Vacation mode – turn it off. In some heating modes, if the temperature is above the maximum or below the minimum recommended, the heat pump won’t operate. If the water heater hasn't been used for two weeks or more, hydrogen gas can accumulate inside the tank – which is very flammable. Before running any of the electrical devices, open the hot water tap for several minutes.
Check the air filter and if it is dirty, clean or replace the filter.
When the demand for hot water is high, heat pump cannot recover fast enough so waiting for the full or partial recovery is the only option. Sometimes it is needed to change the heating mode due to the higher demand and therefore make the pump more efficient. If the water heater runs out of hot water too quick, for example when having guests, when kids get older and they take shower more often (the demand increases) than the issue is with the undersized water heater.
Check for the sediment or mineral build-up in heater’s tank or heating elements – the limescale reduces the heat transfer from the heat source to water. Draining and flushing is usually the best option. Water softeners are good as prevention.
As the unit operates efficiently only in the suggested air temperature range, so when the air gets colder, the unit cannot heat the water to the desired temperature.
The incoming water is way too cold.
During the winter time, the hot water loses the heat rapidly through the water pipes, so the proper pipe insulation is required. The same problem is if the pipe length is too long.
If the unit doesn't work, check the power, fuse, circuit breaker and TCO (manual reset limit) or ECO – requires resetting. Check also for the non-functioning temperature sensor – perform the resistance test and replace it if defective. Replace the heating element if burned out.
If the mixing valve is installed, check is there malfunctioning. Also make sure water connections are not reversed – incoming cold water gets into the hot water pipe and outgoing hot gets in the cold side.
Symptoms and solution:
The thermostat might be set to high or not snug against the tank. A broken thermostat or shorted heating element can also result in extremely high water temperature. If the electronic control is malfunctioning – the best is to call the technician. In order to prevent hot water scald, it is recommended to install thermostatic mixing valve at each faucet.
As said before, some noise from fan and compressor is normal, but if there is a rumbling noise than the problem is with the mineral or sediment build-up on the heating elements. The elements have to be cleaned or replaced. The noises such as the crackling, gurgling or popping are usually related to scale or lime buildup while the pounding noise can be reduced by installing the water hammer arrestor.
The TPR valve is a safety element that should open only if there is an excessive pressure build-up within the closed heating system. It might also be leaking if the debris is stacked inside the valve. During the normal operation the valve should not leak. The thermal expansion is kept under control with the installed thermal expansion tank. In order to limit the water pressure inside the house plumbing, it is beneficial to install the pressure reducing valve - PRV. It should be installed on the cold water supply line to keep the pressure in the range from 50 and 60 psi.
Due to the high content of sulfate in water supplies (usually from well) and its reaction with the anode rod (especially magnesium type), hot water might have rotten egg odor. One of the solutions is to replace the anode with the type that is less prone to this reaction (aluminum) or chlorinate the heater thoroughly.
If milky water is seen, the aerated faucets should be installed to eliminate the buildup gases inside the heating system.
Checking the anode rod regularly or switching to powered anode can also prevent corrosion (that makes water look muddy or brown), as the metal tank is always protected with the effective element, which doesn't deteriorates over time.
Replace the broken compressor or check is there a refrigerant leak. In a case of the AO Smith heat pump, check the run capacitor and look for any damages on the housing. Measure the resistance – if it is indefinite the element has to be replaced.
The first things that need to be checked are the set temperature - which might be high, inefficient heating mode and dirty air filter. Also, if the temperature of the surrounding air is not in the recommending range, the compressor might have trouble operating properly.
The above problems are problems that are found on most of the heat pumps for the residential use… there are many more off course. Due to the advanced electronics followed by the diagnostic system and small display screen implemented in almost every new unit, the error codes are what appear when the problem occurs – making diagnostics easy.
For example, American heat pump uses the error codes such as E20, E21… Bradford White and GE heat pumps use the error codes such as F1, F2… F15, followed by the beeping sound - and each code means something; faulty heating element, dirty air filter, compressor or air failure, sensor malfunctioning …
Every user manual contains the troubleshooting heat pumps guide with the list of the most common diagnostic codes.