Mike the Boilerman -
Your Gas Safe Registered boiler
and central heating repair technician for
London, Thames Valley and south coast
Firstly, the answer the question I pose above is it probably doesn't need powerflushing right now, particularly if a technician is telling you this is the solution to a breakdown. Of the thousands of boilers I've fixed, I have yet to need to carry out a powerflush to fix one.
Starting from the beginning, all the steel components in a heating system (radiators mainly) tend to rust on the inside. The rust forms a black powdery deposit (iron oxide I believe) which forms a gloopy sludge in water and progressively accumulates and collects in the bottom of radiators, pipes and heat exchangers. It prevents radiators from warming up in the centre and at the bottom, it makes heat exchangers in boilers hiss, pop and bang (known as 'kettling') and it reduces the flow capacity of pipes. Therefore it is a Good Thing to have none of this stuff clogging up your heating system.
Clearly it is best not to allow the stuff to occur in the first place and this is done by the installer of the system adding a product called 'corrosion inhibitor' to the circulating water. Even if he does this it tends to get lost should the system be drained down (to move a radiator for example) or if there is a minor leak on the system, which allows the replacement water to dilute the inhibitor to such a degree eventually that it is effectively all lost. Then the corrosion begins to build up.
Once you have a contaminated system, the iron oxide can be removed using the process known as 'powerflushing'. This is where a large pump with a chemical reservoir incorporated is connected into your system and to a drain, and then water with one of a variety of chemicals is pumped around the system at high pressure and high speed. The point of this is to lift all the sludge settled in the system up into suspension in the water, when it is then flushed out into the drain. This may need to be done several times while the pump is connected. It's quite a basic process really but doen well is shockingly time consuming. It used to take me a whole day (working alone) to cleanse a system to my satisfaction back in the days when I used to carry out this sort of work. After cleansing and rinsing, new corrosion inhibitor is then added to stop new corrosion occurring.
However, there is a problem emerging. I regularly hear anecdotes about heating engineers called out to fix boilers pointing out system contamination (usually by drawing off a water sample and showing the customer how black it is) then claiming the breakdown has been caused by the corrosion deposits. The customer is then told they MUST have a powerflush costing many hundreds of pounds carried out before their boiler can be repaired. This is patent rubbish usually as the breakdown will have been caused by something else (a component failure usually), especially if the breakdown occurred suddenly, but it can suit a technician very well to claim corrosion deposits are the problem when he is unsure or unable to trace the real fault. Customers faced with this advice often feel they have no choice but to go ahead with powerflushing but once the flushing has been completed and the fault persists, they are told 'oh well it needed doing anyway'... Which is sort of true really, but the customer has been bounced into having a powerflush that hasn't fixed their breakdown.
It is technically it is hard to criticise advice to powerflush a dirty system but on the other hand it is quite unethical in my opinion to do this instead of persisting and fixing the fault, THEN advising a powerflush as preventative maintenance after the fault has been fixed. In the decade or so I have been specialising in breakdown repair I cannot recall a breakdown where I repaired it by powerflushing. In my experience fixing the underlying failure ALWAYS gets the heating going again with no need for a powerflush to get the heat on. Powerflushing may be advisable but it is rarely if ever, essential for getting the heat back on.
I'm afraid this has turned into a bit of a rant...
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Copyright Michael Bryant 2019
Site first published 16th January 2004
Last updated 11th May 2019
Gas Safe Register 197499, CIPHE registration number 56207