The Davies Craig Booster Pump may be available in the UK, it is a 12 Volt DC
magnetic drive pump that will handle water temps up to 120C. draws approx 1
amp @ 12 volts, has a life in excess 10,000 hours. I have had one running on
one system for over 12 months now with no problems, circulating water
through 7 sq meters of panels located approx 8 meters away from HWC,
connected by 15mm copper pipes.
It is not suitable when in a mains pressure loop, i.e. pressures in excess
of 50 psi as is constructed of a type of plastic.
Would not recommend el-cheapo pumps at all, if your pump stops then things
overheat and cause damage, computer cooling pumps are not rated for
temperatures > 50C.