Smart controls

Smart thermostat not reaching setpoint

Warning Do not attempt any electrical or gas work yourself. Always use a qualified, MCS-certified, or Gas Safe registered professional for repairs.

What you’re seeing (symptoms)

You’ve set your Nest, Hive, or Tado to 21°C, but the room temperature shown on the device (or a separate thermometer) never goes above 19°C, even though the heating is “on.”

What’s normal vs not normal

Normal:

  • A 0.5°C difference between the setpoint and the actual temperature (hysteresis).
  • The room taking 30–60 minutes to reach temperature on a very cold day.

Not normal:

  • The boiler or heat pump running for hours without the temperature rising.
  • The thermostat app saying “Heating” but the radiators are stone cold.
  • The thermostat constantly rebooting or losing Wi-Fi.

Likely causes (ranked)

  1. Poor Placement: The thermostat is in a cold draft or on an uninsulated external wall, making it “think” the room is colder than it is—or vice versa, near a lamp/TV making it think the room is warmer.
  2. TRV Conflict: You have a manual thermostatic radiator valve (TRV) in the same room as the smart thermostat, and it’s set too low, cutting off the radiator before the smart thermostat is satisfied.
  3. Heat Loss exceeds Heat Input: On very cold days, your radiators might not be large enough (or your flow temperature high enough) to overcome the heat escaping through walls/windows.
  4. Signal Issues: The “Link” or “Receiver” near the boiler is losing connection to the thermostat.
  5. Smart Learning: The “True Radiant” or “Optimum Start” feature is still learning your home’s thermal profile.

Quick checks you can do safely

  • Ensure all manual TRVs in the room with the thermostat are set to “MAX” or “5.”
  • Move the thermostat to a different spot in the room (if it’s wireless).
  • Check the batteries in the thermostat unit.

When to call an installer

  • If the app shows the heating is on, but the boiler/heat pump is not firing up.
  • If you suspect the wiring to the boiler receiver has come loose.
  • If your system is constantly “overshooting” or “undershooting” by more than 2°C.

Questions to ask your installer

  • “Is the thermostat positioned in the optimal ‘reference’ room?”
  • “Is the boiler’s maximum flow temperature set high enough for the depths of winter?”
  • “Should we consider smart TRVs in every room for better control?”

Related NetZeroNow tools & guides

FAQs

Where should my thermostat be? Ideally on an internal wall, about 1.5m high, away from direct sunlight, drafts, and heat sources like radiators or electronics.

Why does it say ‘2 hours to target’? Smart thermostats calculate how long your specific home takes to warm up. If it’s consistently wrong, the device may need to be reset to “re-learn” your home.

Can I have two thermostats? Yes, if your home has “zones” (e.g., upstairs and downstairs), you will need a separate smart thermostat for each zone.

Does it work with heat pumps? Yes, but you should avoid “setback” temperatures (turning the heat way down at night), as heat pumps take much longer to recover the temperature than boilers.

What is ‘TPI’ control? Time Proportional & Integral. It’s a way the thermostat “pulses” the boiler on and off as it nears the target temperature to prevent overshooting.

Written by NetZeroNow | Last updated on 2026-03-02