My Mira 723 shower only puts out cold water. It has direct 22mm supplies from the H&C water tanks. A friend says it is probably a broken thermostat. I am remodelling the shower room and want the most cost effective solution. My options appear to be: 1) buy a new shower valve (expensive); 2) replace the thermostat component; or 3) fit a second hand Aqualisa valve a friend has given me - looks like a Classic Aquavalve 200/400 (cheapest – appears to need only new supply connectors, but concerned whether I will be able to easily fit valve to the existing supply pipe configuraion and am not sure how long I can expect an old valve to keep working).

I want to do the work myself (am a fairly experienced DIYer) and would be grateful for some guidance.