Heat Pump Not Heating? Troubleshooting Guide

Step-by-step guide to diagnose and fix common heat pump problems. Same-day emergency service available across Dorset.

Emergency: 01202 985350

Quick Diagnostic: What's Happening?

Not Working At All

No lights, no sound, completely dead. Likely power issue.

Blowing Cold Air

System running but air from vents is cold or cool.

Not Hot Enough

Running but house not reaching desired temperature.

Keeps Cycling On/Off

Turning on and off repeatedly, short-cycling.

Heat Pump Not Working At All

System completely dead - no lights, no sounds, no operation.

✅ DIY Checks (Try These First)

1. Check Circuit Breaker
  • •Locate electrical panel
  • •Check heat pump breaker hasn't tripped
  • •If tripped, reset once only
  • •If trips again immediately, call for service
2. Verify Power Supply
  • •Check outdoor unit has power light on
  • •Confirm indoor unit display is active
  • •Test if other circuits in house working
  • •Check for blown fuses
3. Thermostat Check
  • •Replace thermostat batteries if wireless
  • •Verify thermostat display is on
  • •Check thermostat is in 'Heat' mode
  • •Try turning system fully off then on
4. Emergency Shutoff Switch
  • •Check indoor shutoff switch isn't accidentally off
  • •Verify outdoor isolator switch is on
  • •Look for red emergency shutoff near indoor unit

Call Service If:

  • Circuit breaker trips repeatedly
  • No power to unit despite breaker on
  • Burning smell or sparking
  • Error codes displayed on unit

Heat Pump Blowing Cold Air

System running but air from vents/radiators is cold or lukewarm.

ℹ️ Normal vs Problem

✅ NORMAL: Defrost Cycle

Every 30-90 minutes in cold weather, heat pump reverses briefly (2-10 mins) to melt ice from outdoor unit. This temporarily blows cool air - completely normal!

❌ PROBLEM: Constantly Cold

If continuously blowing cold air for 15+ minutes with no warm periods, there's a fault.

✅ DIY Checks

1. Thermostat Mode
  • •Verify set to 'Heat' not 'Cool'
  • •Check temperature set ABOVE current room temp
  • •Try increasing setpoint by 5°C
  • •Ensure not in 'Auto' mode switching to cooling
2. Air Filter (if air-to-air)
  • •Turn system off
  • •Remove and inspect air filter
  • •If dusty/dirty, wash or replace
  • •Blocked filters reduce heat output by 30-50%
3. Outdoor Unit Inspection
  • •Check for heavy ice buildup (more than light frost)
  • •Clear any snow or debris blocking airflow
  • •Ensure unit has 1m clearance all around
  • •Listen for compressor running (low hum)
4. System Reset
  • •Turn off at thermostat
  • •Switch off circuit breaker for 60 seconds
  • •Turn back on and wait 5 minutes
  • •Restart heating mode

🔧 Likely Issues Requiring Service:

  • Low refrigerant: Leak causing insufficient heating capacity
  • Reversing valve stuck: System stuck in cooling mode
  • Compressor failure: Not compressing refrigerant properly
  • Faulty defrost cycle: Not switching back to heating after defrost

House Not Reaching Temperature

Heat pump running continuously but house won't get warm enough.

✅ DIY Checks & Adjustments

1. Flow Temperature
  • •Access heat pump controls/settings
  • •Check flow temperature setting
  • •If below 45°C, increase to 50-55°C
  • •Higher temps heat house faster but reduce efficiency
2. Thermostat Settings
  • •Lower expectations: heat pumps deliver gradual heat
  • •Give system 2-3 hours to reach temperature
  • •Check radiators are hot throughout (not lukewarm)
  • •Verify all thermostatic radiator valves open
3. Insulation & Draughts
  • •Check for open windows/doors
  • •Seal obvious draughts around doors/windows
  • •Close curtains at night (10-15% heat retention)
  • •Ensure loft hatch is sealed
4. Radiator Air Bleed
  • •Turn heating off
  • •Use radiator key to bleed each radiator
  • •Release air until water appears
  • •Top up system pressure if needed (1-1.5 bar)

🔍 Professional Assessment Needed If:

  • System undersized: Heat pump capacity insufficient for property
  • Radiators too small: Not enough surface area for heat output
  • Refrigerant low: Slightly low charge reduces capacity 20-40%
  • Poor insulation: Heat loss exceeds heat pump output

Heat Pump Cycling On/Off Repeatedly

System turning on and off every few minutes (short-cycling).

✅ Quick Fixes

1. Air Filter Blockage
  • •Severely blocked filter is #1 cause
  • •Remove and inspect filter
  • •Clean or replace immediately
  • •Check monthly during heating season
2. Thermostat Location
  • •Check thermostat not in draft or near heat source
  • •Ensure not in direct sunlight
  • •Should be on internal wall, 1.5m height
  • •Away from radiators, fireplaces, kitchen
3. System Pressure
  • •Check pressure gauge on indoor unit
  • •Should read 1-1.5 bar
  • •If below 0.5 bar, top up via filling loop
  • •If above 2.5 bar, may need bleeding

⚠️ Service Required For:

  • Oversized system: Heat pump too powerful for property (professional assessment)
  • Refrigerant issues: Incorrect charge causing pressure cycling
  • Faulty pressure switches: Sensors triggering unnecessary shutdowns
  • Control board malfunction: Electronics sending incorrect signals

Short-cycling causes excessive wear and reduces lifespan. Call for service promptly to prevent damage.

When to Call Professional Service

🚨 Emergency Service (Same Day)

  • No heating in freezing weather
  • Water leaking from unit
  • Burning smell or smoke
  • Loud banging or grinding noises
  • Ice completely covering outdoor unit
Emergency: 01202 985350

🔧 Standard Service (Next Day)

  • Reduced heating performance
  • Short-cycling (on/off repeatedly)
  • Error codes displayed
  • Higher than normal energy bills
  • DIY checks haven't resolved issue

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