Water Source Heat Pump Not Heating: Troubleshooting and Fixes

The following guide explains why a water source heat pump not heating occurs, how to diagnose root causes, and practical fixes homeowners and building managers can apply. The content focuses on common fault patterns, testing steps, maintenance tips, and when to contact a licensed technician.

Symptom	Likely Cause	Quick Action
Weak or No Heat	Low refrigerant, compressor fault, or insufficient water flow	Check water flow, listen for compressor, inspect coils
Intermittent Heating	Control cycling, dirty filters, or pump issues	Monitor cycles, clean filters, test pump pressure
Frozen Coils	Poor water chemistry or low flow	Shut unit off, defrost, test loop flow

How Water Source Heat Pumps Work

Water source heat pumps transfer heat between indoor spaces and a water loop using a refrigerant cycle. A compressor, expansion valve, evaporator, and condenser work together to extract or reject heat. The water loop (open or closed) supplies or absorbs heat from the refrigerant via a heat exchanger. Proper operation requires correct refrigerant charge, adequate water flow, functional controls, and good heat-exchanger cleanliness.

Common Causes For A Water Source Heat Pump Not Heating

Several system areas commonly produce heating failures. Refrigerant issues such as leaks or incorrect charge reduce heat transfer. Water loop problems like low flow, pump failure, blocked strainers, or poor water chemistry also prevent heat exchange. Mechanical failures include compressor motor faults, faulty reversing valves, or failed reversing valves in heat-pump systems. Controls and electrical problems—thermostat, relays, fuses, contactors, or sensors—can stop heating cycles or cause improper staging.

Initial Diagnostic Steps

Perform a methodical check to isolate the problem. Safety first: shut power when accessing electrical components. Use basic tools: multimeter, pressure gauges, infrared thermometer, and flow meter if available. Begin with simple checks to avoid unnecessary repairs.

1. Confirm Thermostat And Controls

Verify the thermostat is set to heat mode and the setpoint is above room temperature. Check for error codes on the unit display or building automation system. Reset the thermostat and observe whether the unit attempts to start. If controls show faults, record codes for technician reference.

2. Verify Power And Electrical Components

Confirm the unit receives correct voltage at the disconnect. Inspect fuses, breakers, contactor coil continuity, and any safety interlocks. A dead compressor often traces to a tripped breaker, blown fuse, or faulty contactor. Use a clamp meter to verify inrush amps and running current against nameplate ratings.

3. Check Water Loop Flow And Temperature

Measure supply and return water temperatures at the unit. A typical temperature differential across a working heat exchanger ranges between 5°F–15°F depending on load. No or a small delta may indicate insufficient heat transfer. Inspect the pump operation, valves, strainers, and for air locks. Low flow is a very common reason for lack of heating.

4. Inspect Coils And Filters

Dirty evaporator or condenser coils and clogged air filters reduce heat transfer and airflow, causing poor heating. Clean coils and replace filters as needed. For units with finned coil packs, straighten bent fins and remove debris. Check coil fins for frost accumulation which can indicate refrigerant or flow problems.

Refrigerant And Compressor Issues

When a water source heat pump not heating stems from the refrigerant side, it often means a leak, incorrect charge, or compressor failure. Signs include abnormal suction/discharge pressures, warm suction lines, or oil stains near service ports.

Refrigerant Leak Or Incorrect Charge

Low refrigerant reduces heating capacity. Measure pressures with gauges and compare to manufacturer charts for the current ambient and water-loop conditions. Look for oily residue or dye near fittings. Refrigerant repairs require EPA-certified technicians; a partial charge may mask the problem but will reduce heating performance and increase energy costs.

Compressor Problems

A failing compressor can hum, click, or not run at all. Locked rotor or mechanical failure may need compressor replacement. Evaluate start capacitors and relays before replacing the compressor. If the compressor runs but is weak, perform a full refrigerant and electrical inspection to determine root cause.

Water Loop And Hydronic Issues

Because a water source heat pump depends on the water loop, issues here are common causes of a water source heat pump not heating. Problems include pump failure, blocked heat exchangers, incorrect pump sizing, and poor water chemistry that fouls coils.

Pump Failure And Valve Problems

Confirm the loop pump(s) are running and producing adequate head. Bypass valves or isolation valves may be incorrectly positioned. Air trapped in the loop reduces flow and heat transfer; bleeding air and verifying proper expansion tank function helps maintain loop integrity.

Scale, Corrosion, And Fouling

Hard water and improper treatment cause scale and corrosion that reduce heat-exchanger effectiveness. Inspect for restricted flow in shell-and-tube or plate heat exchangers. Consider water treatment, chemical cleaning, or replacement of fouled components to restore heat transfer.

Controls, Sensors, And Reversing Valve

Controls problems can mimic mechanical issues. Faulty temperature sensors, pressure transducers, or a stuck reversing valve (in heat-pump modes) may stop heating or cause incorrect mode operation.

Thermostat And Sensor Calibration

Test sensor readings at the controller and compare to independent thermometers. Replace or recalibrate sensors that report inaccurate temperatures. Software or configuration errors in building automation systems can mismanage setpoints or staging logic.

Reversing Valve And Defrost Cycle

In heat-pump systems, a stuck or miswired reversing valve will prevent switching to heating mode. Listen for valve actuation and verify coil voltages during mode change. Improper defrost control can also reduce heating if the unit remains in defrost too long.

Frozen Coils And Defrosting

Frozen outdoor or hydronic coils indicate low flow, refrigerant imbalance, or inadequate defrost controls. If coils are frozen, power down the unit and allow natural thawing; do not force heat. Once thawed, pursue inspection for the underlying cause instead of merely restarting the unit repeatedly.

Maintenance Steps To Prevent Heating Failures

Regular maintenance reduces the probability of a water source heat pump not heating. Schedule seasonal inspections, clean coils and strainers, verify refrigerant charge annually, and maintain proper water chemistry.

• Quarterly: Change air filters, inspect drain pans, and check controls.
• Semiannually: Clean coils, check electrical connections, and test pumps.
• Annually: Perform refrigerant leak checks, flush water loops if necessary, and record performance baselines like supply/return deltas.

Troubleshooting Checklist

Check	What To Look For	Action
Thermostat	Mode, setpoint, wiring	Reset/calibrate or replace
Power	Voltage, breakers, fuses	Restore power, replace fuses
Compressor	Run/no run, amps	Test capacitors, relays, replace if faulty
Refrigerant	Pressure, oil residue	Call EPA-certified tech for repair
Water Flow	Pump operation, delta T	Repair pump, bleed air, clear strainers
Coils/Filters	Soiling, frost	Clean or replace

When To Call A Professional

Some issues require licensed HVAC or plumbing professionals. Refrigerant handling, compressor replacement, complex electrical faults, and major water-loop repairs should be handled by qualified technicians. If basic troubleshooting—verifying power, filters, and flow—does not restore heating, schedule service to avoid further damage and ensure safe, code-compliant repairs.

Estimated Repair Costs And Timeframes

Costs vary widely depending on the root cause. Minor fixes like filter replacement or thermostat recalibration may be under a few hundred dollars. Refrigerant leaks, control board replacement, or pump repairs typically range from a few hundred to a few thousand dollars. Compressor replacement and major water-loop refurbishing can be several thousand dollars. Diagnostic visits often take 1–3 hours; major repairs may require multiple days if parts or loop work is involved.

Energy And Performance Considerations

Reduced heating performance often increases energy consumption as the system runs longer to meet setpoints. Restoring proper refrigerant charge, flow, and clean heat exchangers improves coefficient of performance (COP) and lowers operating cost. Investing in preventive maintenance yields predictable performance and energy savings.

Key Safety And Compliance Notes

Work on water source heat pumps involves electrical and refrigerant hazards. Only qualified personnel should handle high-voltage components and refrigerants. Follow local codes for refrigerant handling and disposal. Maintain documentation of repairs and charges to support warranty claims and future troubleshooting.

Additional Resources And Manufacturer Guidance

Consult the unit’s manufacturer manual for specific diagnostic codes, pressure-temperature charts, and part numbers. Building automation systems and facility maintenance logs help identify recurring problems. For complex installations, consider hiring a contractor experienced in water-source heat pumps and hydronic systems.

Quick Reference: Immediate Actions If Not Heating

1. Verify thermostat settings and circuit power.
2. Check air filters and clear visible blockages.
3. Confirm water-loop pump operation and measure supply/return delta T.
4. Listen for compressor operation and note unusual noises.
5. If coils are frozen, power down and allow thaw before further inspection.
6. Contact a licensed technician for refrigerant, compressor, or major electrical issues.

Following these steps helps identify why a water source heat pump not heating is occurring and directs correct fixes while avoiding common misdiagnoses. Proper diagnostics, routine maintenance, and timely professional repairs restore heating performance and preserve system life.