Overview
The "FLASH OFF FLASH" display on a Baxi Solo typically indicates an electrical supply problem — most commonly an undervoltage condition where the incoming mains voltage has dropped below a safe operating threshold (your note suggests below about 180 V). The boiler’s electronics detect the low supply and either lock out or refuse to run to protect internal components and prevent unreliable operation. Severity: this fault will prevent the boiler from operating normally (no heat or hot water) but is not usually immediately dangerous in itself. However, persistent undervoltage or repeated attempts to run the boiler on a poor supply can stress the PCB and other electronics and could lead to further faults. Whether this is DIY or professional: start with basic safety checks and simple resets you can do at home, but measuring mains voltage, tracing wiring faults or repairing internal components should be left to a qualified electrician or a Gas Safe engineer. If you smell gas or see damage, isolate the appliance and call a professional immediately.
Possible Cause: Voltage less than 180V
Troubleshooting Steps
Safety precautions:
1) If you ever smell gas, evacuate, turn off the gas supply at the meter if safe to do so, do not operate electrical switches, and call the gas emergency service or a Gas Safe engineer immediately.
2) If you are not confident working around mains electricity, do not open the boiler or attempt live electrical tests — contact a qualified electrician.
3) Before opening any boiler covers, switch off the electrical supply to the boiler at the isolator and the consumer unit. Only restore power for live checks if you are competent and using appropriate test equipment.
Initial checks a homeowner can do:
1) Check whether other appliances or lights in the house are dimming or behaving unusually—this can indicate a general low voltage or supply problem.
2) Check the house consumer unit for tripped breakers or RCDs and reset them if safe and appropriate.
3) Check the boiler’s display and controls and make a note of the exact message or any flashing pattern and the boiler model/serial for the engineer.
4) Try a controlled reset: follow the Baxi reset method for your model (press reset button or turn selector to R and hold for ~3–5 seconds). Do not repeatedly attempt resets if the fault returns.
Specific diagnostic and fix steps (what to try and what the engineer will do):
1) If the fault follows a brief mains glitch and a single reset clears it, monitor the boiler. If it recurs, do not keep resetting repeatedly.
2) If you suspect a local supply problem (multiple appliances affected or lights dim), contact your electricity supplier to report a potential low-voltage/brownout issue.
3) If you are competent with electrical testing and suitably equipped: with the boiler powered and safe to access, an electrician or qualified engineer should measure the incoming mains voltage at the boiler L and N terminals. The boiler is likely to flag a fault if voltage is below ~180 V. Do not attempt live voltage tests if you are not trained.
4) An engineer will also check the boiler’s mains wiring, the fused spur/isolator, and the internal mains fuse/PCB power supply for loose connections or damage. They will inspect the PCB for signs of stress or burned components caused by undervoltage events.
5) If a faulty internal power supply or PCB damage is found, replacement and repair must be carried out by a Gas Safe registered engineer or qualified electrician following manufacturer guidance.
6) If the electricity supply is stable at the meter but low only at the property or boiler, an electrician will investigate local supply wiring, connections, and the consumer unit. If the supplier confirms low mains at the feed, they will need to resolve it.
When to call a professional:
1) Call a qualified electrician if you suspect a mains voltage issue and for any voltage measurements, wiring checks or repairs.
2) Call a Gas Safe registered heating engineer if the fault persists after supply checks, if the boiler shows further electrical/PCB faults, if internal components need replacing, or if you smell gas.
3) Provide the engineer with the exact error pattern, model/serial numbers and any observations (lights dimming, frequency of fault) to speed diagnosis.
Final notes:
1) Do not attempt internal electronic repairs yourself — PCBs and mains wiring are hazardous and require trained personnel.
2) Avoid repeated resets; a one-off reset after checks is acceptable but repeated lockouts indicate an underlying fault that needs professional attention.
3) Keep records of when the fault started, any power events, and what you tried — this helps electricians and engineers diagnose whether the issue is an external supply problem or internal boiler fault.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi Solo.