Hello and welcome! I'm Billy and i will assist you with this.
My apologies for the delay, thank you for your patience.
The most likely reason for the light flashing would be a small leak within the system, causing coolant
(water) level to drop and the light to illuminate.
The second likely reason would be the cap, it can leak under pressure.
The water pump could cause this, and other problems such as a leaky head gasket (blown), or other.
But in you case, i would replace the cap (expansion vase cap, the one you open to top up). And then, if the problem persists, i woudl have the system pressurized and check it for leaks (as under pressure the water leak would be more visible). While at it, i would flush the system, and pour in clean water, until the system is clean (with the heater on max heat), and then fill with coolant, and take it from there...
Kindly get back to me with your findings, or if further assistance is needed, so we proceed accordingly.