Expect to pay up to £1,500 for a new boiler in a new position see our guide to the cost of installing a boiler for more guidance on. Your central heating system will also need to be flushed, so don’t forget to factor in the cost of a powerflush, which typically costs around £375 and a new magnetic filter; a unit that traps sludge, dirt and debris and will help increase the efficiency and life of your central heating system you may also need new trvs (thermostatic radiator valves). Your.