No Hot Water from a Heat Pump – Causes, Checks, and What to Do Next
Losing hot water is one of the most frustrating heat pump problems. Unlike heating issues, hot water faults are often caused by controls, settings, or scheduling rather than a major system failure.
This guide explains the most common reasons a heat pump produces no hot water, what you can safely check yourself, and when it’s time to call an engineer.
How heat pumps normally make hot water
Most heat pumps heat hot water using a hot water cylinder with an internal coil. The heat pump periodically switches from space heating to hot water mode to reheat the cylinder.
Hot water operation is usually controlled by:
- A hot water schedule or timer
- A cylinder temperature sensor
- System priority settings
- Occasionally an immersion heater
If any of these are incorrect or disabled, you can end up with no hot water even though the heat pump appears to be working.
Common symptoms
- No hot water at taps
- Water briefly warm then running cold
- Hot water works sometimes but not consistently
- Heating works but hot water doesn’t
- Heat pump runs but cylinder stays cold
Most common causes of no hot water
Hot water schedule turned off
One of the most common causes is the hot water schedule being disabled or set incorrectly. This often happens after power cuts, servicing, or controller changes.
Cylinder already “thinks” it is hot
If the cylinder sensor is faulty or misplaced, the system may believe hot water is already available and refuse to heat it further.
Hot water priority disabled
Many systems give hot water priority over heating. If this setting is turned off, space heating may prevent hot water from being reheated.
Immersion heater switched off or failed
Some systems rely on an immersion heater as backup or for high-temperature hot water. If it is switched off or faulty, you may notice a lack of hot water.
Flow or circulation problems
Blocked filters, air in the system, or closed valves can prevent hot water from being transferred into the cylinder.
What homeowners can safely check
You can check:
- Hot water is enabled on the controller
- The hot water schedule is active
- The cylinder target temperature is reasonable (typically 45–55°C)
- Any boost or one-time hot water function
- The immersion heater switch (if fitted)
Try running a manual hot water boost if your controller allows it, and wait at least 60–90 minutes before judging the result.
Things that look like faults but aren’t
- Hot water scheduled for overnight only
- Long gaps between hot water reheats
- Heat pump prioritising heating during cold weather
- Lower hot water temperatures compared to boilers
Heat pumps reheat water slowly and efficiently — this is normal behaviour.
When no hot water points to a real problem
You may have a fault if:
- The cylinder never warms up
- Error codes related to hot water appear
- The heat pump never switches into hot water mode
- Boost functions make no difference
- The system previously worked and has suddenly stopped
When to call an engineer
Contact a qualified heat pump engineer if:
- You’ve checked schedules and settings with no success
- The immersion heater or cylinder sensor may be faulty
- There are flow or circulation faults
- Error codes persist
- The system has never produced reliable hot water
Hot water issues are often quick to diagnose once settings and sensors are checked.
Key takeaway
No hot water from a heat pump is usually a control or scheduling issue, not a major breakdown.
Check settings, schedules, and boost functions first. If the cylinder still doesn’t heat, professional diagnosis is the safest next step.