If your 091FLRFv2 thermostat shows flickering backlight or briefly displays the low battery icon, even when using new batteries – don't panic. This is a known behavior, and often perfectly normal.
1. Power supply and LCD behavior
The thermostat uses 2x AA 1.5V alkaline batteries. The screen lights up when the OK button is pressed and turns off automatically after a few seconds.
Do not use rechargeable batteries (NiMH/NiCd) – their 1.2V output can cause false low- battery readings.
2. What causes flickering backlight?
Flickering may happen:
- When changing settings rapidly
- During automatic radio sync with RXRT510
- If there's a temporary voltage drop under load
As long as:
- the screen doesn't go completely blank,
- the buttons work,
- and the battery icon disappears quickly,
…it’s not a fault.
3. Why did the battery icon appear and disappear?
The icon can show briefly if:
- voltage dips below 2.2 V temporarily
- the batteries are new but low-quality or low-capacity
- contact in the battery slot is imperfect
If the icon disappears and device works fine – no action is needed. This is part of the energy-saving and voltage-testing algorithm.
4. How to prevent this behavior?
- Use high-quality alkaline batteries (e.g. Duracell, Energizer)
- insert batteries properly and ensure tight fit
- Avoid pressing multiple buttons rapidly
- Install thermostat away from sunlight, drafts, or cold walls – this affects sensor load
5. When to contact support
Reach out only if:
- icon stays on permanently
- display turns off or becomes unresponsive
- no signal is received by RXRT510 despite proper pairing