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My Thermostat Has No Display or Is Completely Blank

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What this article covers

This article explains what to do when a thermostat has no display at all.

Use this article if:

  • The thermostat screen is completely blank.
  • There are no numbers or symbols showing.
  • There is no Power icon showing.
  • The thermostat will not switch on.
  • Multiple hard-wired thermostats have lost their displays.

This article covers both:

  • Battery-powered thermostats.
  • Hard-wired thermostats.

What this article does not cover

This article does not cover:

  • A thermostat showing offline in the Heatmiser app.
  • A thermostat that has a display but is not responding correctly.
  • A thermostat that will not pair.
  • A thermostat disappearing from the app.
  • A neoHub showing offline.
  • A blank display caused by intentionally switching the thermostat off when it can still be switched back on normally.
  • Wiring or replacing internal components without a qualified electrician or heating engineer.

Part 1: Check Whether the Thermostat Is Switched Off

If the thermostat screen is completely blank, first try switching it back on.

  1. Press or tap the Power button.
  2. Check whether the display comes back on.

If the thermostat switches on and the display operates normally, no further troubleshooting is required.

If the display remains completely blank, continue to Part 2.

Part 2: Does the Thermostat Have a Battery Tray?

Look at the bottom of the thermostat.

If there is a removable battery tray, the thermostat is battery powered.

Continue to Part 3.

If there is no battery tray, continue to Part 4 for hard-wired thermostats.

Part 3: Battery-Powered Thermostat Has No Display

If the thermostat has a battery tray:

  1. Push the battery tray upwards to release it.
  2. Remove the battery tray.
  3. Replace the batteries with new AAA batteries.
  4. Refit the battery tray.
  5. Check whether the thermostat display comes back on.

If the display comes back on, no further troubleshooting is required.

If the thermostat remains completely blank after fitting new batteries, there are no further troubleshooting steps in this article.

Please speak to an adviser who can assist further.

Part 4: Hard-Wired Thermostat Has No Display

If the thermostat does not have a battery tray, it may be powered from the heating controls.

The next checks depend on the type of heating system.

Electric Underfloor Heating

If the thermostat controls electric underfloor heating:

  1. Check that the fused spur supplying the thermostat is switched on.
  2. If possible, check whether any other thermostats supplied from the same circuit are also blank.
  3. If the fused spur is switched on but the thermostat remains completely blank, the electrical supply to the thermostat needs to be checked.

At this point, a qualified electrician should investigate the electrical supply and thermostat.

Water Underfloor Heating

If the thermostat controls water underfloor heating, look for the wiring centre that the thermostats are connected to.

Check whether the wiring centre has power or indicator lights showing.

If the Wiring Centre Has Power

If the wiring centre is powered but the hard-wired thermostat remains completely blank, there may be a problem with:

  • The wiring between the wiring centre and thermostat.
  • The thermostat's backplate or power supply.
  • The thermostat itself.

A qualified electrician or heating engineer should check the supply at the thermostat before replacing components.

Replacement Backplates

If testing confirms that the thermostat backplate has failed, replacement backplates are available from the Heatmiser Shop for the following thermostats:

  • neoStat V2
  • neoStat V3
  • Slimline V4

This means the whole thermostat may not need replacing if the fault is confirmed to be with the backplate.

The electrical supply and wiring should be checked before replacing the backplate.

If the Wiring Centre Has No Power

If the wiring centre has no lights showing:

  1. Check that the fused spur supplying the wiring centre is switched on.
  2. If the fused spur is on but the wiring centre remains completely unpowered, an internal fuse may have blown.

An internal fuse can blow because of a fault elsewhere on the heating system.

Possible causes include:

  • Faulty actuator.
  • Faulty pump.
  • Faulty valve.
  • Faulty thermostat.
  • A fault with the wiring centre itself.

Do not simply replace the fuse without investigating why it failed.

A local electrician or heating engineer should test the wiring centre and connected components first. Replacing a fuse without identifying an existing electrical fault could result in further damage.

Information for Electricians and Heating Engineers

The following information is intended for a qualified electrician or heating engineer.

5A Fuse

Replacement specification:

Quick Acting F HBC Fuse 5A 5x20

RS number: 537-1408

2A Fuse

Replacement specification:

Quick Acting F HBC Fuse 2A 5x20

RS number: 537-1177

800mA Fuse

Replacement specification:

FST 5x20 Fuse F, L, 800mA 250VAC

RS number: 541-4369

The wiring centre and connected components should be checked for faults before replacing an internal fuse.

If All Hard-Wired Thermostats Are Blank

If all of the hard-wired thermostats have gone blank at the same time, do not assume that every thermostat has failed.

Check the common power supply first.

For a water underfloor heating system:

  1. Check whether the wiring centre has power.
  2. Check that its fused spur is switched on.
  3. If the wiring centre has no power despite the fused spur being on, have an electrician or heating engineer investigate the supply, internal fuse and connected components.

Multiple thermostats losing their displays at the same time can indicate a problem with the common electrical supply rather than individual thermostat failures.

What Happens Next

If replacing the batteries or restoring the electrical supply brings the thermostat display back on, no further action is required.

If a battery-powered thermostat remains blank with new batteries, please speak to an adviser.

If a hard-wired thermostat remains blank despite having the correct electrical supply, a qualified electrician or heating engineer should investigate the thermostat, backplate and wiring.

If the wiring centre has lost power, a qualified electrician or heating engineer should identify the cause before replacing an internal fuse.

If these checks have been completed and the cause has not been identified, the guidance in this article has no further troubleshooting steps. Please speak to an adviser who can assist further.

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