Boiler noises are often caused by scale or debris accumulating on heat transfer surfaces, thus preventing the  water from carrying away heat from the metal surface. This means that the metal runs hotter than design temperature and may even exceed 100 degrees C.

The layer of scale / debris is never even, and there will be areas where the water contacts metal above 100 degrees. At this temperature water flashes into steam, increasing its volume by almost 1500 times. The steam bubbles then move away from the high temperature zone and collapse and it is the sound of the implosion of the steam bubble that you hear. This phenomenon is most likely to occur when the boiler first fires and is working hard.

It is a reasonable assumption that if you can remove the debris / scale (and you usually can when power flushing) that you will remove the problem.

Having said that, we know that boilers with cast iron heat exchangers can acquire corrosion pits as they age, generally if the water treatment has been inadequate. In these areas, where the heat exchanger metal is reduced in thickness, the heat flux can be higher than the designer intended, and there can still be boiler noises no matter how clean the heat transfer surface may be after a power flush.

The cold spot on a rad, usually in the middle bottom area, is a result of corrosion debris from the metal in your heating system being deposited In the form of a sludge [Iron Oxide], this sludge deposit forms in areas with low water flow, middle of rads or on pipe branched connections. Cold areas on rad, loss of heat to individual rads and even loss of heating to entire circuits.

There are two reasons for corrosion, oxygen and electrolyse

The main reasons we find high levels of oxygen in heating system.

• Heating water flowing trough the feed and expansion [f & E] tank in your attic, this mainly occurs in a duel fuel heating system, where the pipe and pump connections are incorrectly positioned in the circuits. This is easily recognised, by viewing the F & E tank while the system is heating normally, this tank will be getting hot and water may be pitching from the vent pipe into the tank.
• Houses built around the early 2000’s, in some cases these newly built houses having used a plastic piping which did not have an oxygen barrier inbuilt into piping. This piping allows the diffusion and absorption of oxygen through the piping into the central heating waters. An analysis of the system will verify if you have this piping, following a powerflush and going forward an annual dose of inhibitors will prevent the rise in oxygen levels.
• Continuous topping up of central heating pressure, adding top-up pressure is essential for the operation of a sealed heating system, when adding top-up water to your system this water contains oxygen. Problems only occur when top-up valve is constantly open to mask a central heating leak from a safety valve or pipe leak. The leak should be addressed otherwise you will have a corroded and leaking central heating system.

Electrolytic corrosion.

Electrolytic corrosion occurs when two dissimilar metals conduct a very small electrical current using the central heating water as a conductor.

We generally see this problem in ‘gun barrel’ systems where copper piping is used to connect equipment to the steel gun barrel piping.

This is generally not an issue in the more modern homes and where plastic piping is used for main circuits of the heating system.

Sometimes we may have to remove a radiator, bring outside and rinse it thoroughly. We only do this if we are unable to breakdown the sludge using the power flushing machine.

Magnetic filters are an excellent device to be fitted to your heating system, after the power flush fitting a mag filter will stop sludge depositing in your rad and heating system. The mag filter requires maintenance cleaning and is great for using as a dosing pot to top-up the inhibitor levels in you heating system.

Every time you upgrade to a new boiler, or if you have flow issues, blocked rads or cold spots on your rads.

In more that 15 years of power flushing we only have had 2 or 3 radiators leak while powerflushing, power flushing will not cause a leak but will speed up the leaking process to an already internally corroded or damaged radiator.

Power flushing is low pressure [1 bar or less] but instead uses high velocity flow of water [90 litres per minute] to remove sludge from rads, boiler and piping.

We have previously metered some varying sized power flushing jobs, water usage between 2 and 3 thousand litres are used. We have now implemented some new procedures and equipment to reduce water consumption to 1500liters for the average power flush.

What we will generally do in this circumstance,  check all other possibilities, rule out the issue is not coming from a failing circulating pump also we will complete a full balance of the radiators, after this an some other testing will determine if a power flush is required.