It is a bit of a myth that a powerflush may cause a leak, we fit more than a hundred boilers a year and powerflush every time. Anything that may leak during a powerflush is going to leak in the very near future anyway, but even this is very rare. Maybe 1 in 150. It is absolutely critical we get the system clean for the new boiler, old boilers will work fine with some sludge in the system. Good modern condensing boilers are reliable but only is the system is clean. The heat exchangers are large but contain little water which is forced through small passage ways. This is what gives the efficiency. The only way we can be certain of cleaning this system is to powerflush it.
We offer every customer we fit a boiler a central heating care plan. This guarantees the entire central heating system so if a leak does occur we will fix it without cost to you, this coverage is £10 per month includes the annual boiler service and you can cancel it whenever you want with 1 month notice. So confident about the low chance of a leak being caused we can offer you this before we powerflush.
Every installer has their own standards, however we will only fit a boiler if we can be certain we have done everything possible to ensure the reliability of the boiler. Vaillant or Worcester never get called out to our system because we have left sludge in the system.