What's the going rate to install a 15mm flow and return to a radiator to an adjacent room roughly 3m away from the boiler? Boiler's in the kitchen and flow and return needs running to the extension which I've converted into a bathroom - both on the same floor. I've got a modern Vailant combi boiler. Pipes look easy enough to conceal behind kitchen units. Got a quote here for £400-500 but potentially more.