When your friendly plumber installs a new heat pump boiler it should be normal practice for him/ her to flush the existing pipe work and radiators to make sure the system is clean before connecting the new kit. Many manufacturers will void your warranty if this hasn't been done.

All heating systems suffer from corrosion over time and often some scale build up. If you slap a new boiler onto an old system potentially these contaminants can end up returning to the boiler and blocking the heat exchanger.

Back in the old days this wasn't a problem as the heat exchangers had large passes through them so the sediment etc just flushed through. Nowadays all systems use tiny heat exchangers with passes of less than 3mm wide which can easily be blocked.

When it comes to the radiators, if they are full of sediment their performance really suffers. It is for this reason that the Building Regulations for England and Wales, Part L 2006, now require a central heating system to be cleaned and inhibited chemically whenever the boiler is changed or any major works are carried out to the system. There is even a standard laying out how this flushing should be done, BS 7593:2006

The recommended procedure is to power flush the system in both forward and reverse directions at 110% or more of the normal flow rate and to use a chemical flushing agent where required. Now to do this procedure properly takes a little time usually about a day for a 4-bed house.

Power flushing to be honest is a license to print money, most people are charging in excess of £400 to carry out this service. It's not the most skilled of jobs and the hardware required to be a power flusher is about £1000.

To put this into context a very experienced commissioning engineer for VRV and chillers will charge about the same day rate. The best bit is, you don't need to be gas safe registered or a qualified refrigeration engineer, in fact you don't need any qualifications at all.

There is no recognized procedure or certification, so you can pretend to be the man who can and give a certificate at the end to prove it. Any one with a computer can set this up.

I'm beginning to think I should pack this in and become a power flusher.