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A rough guide to power or chemical flush diagnostics.



To Flush or not to flush that is the eternal flushing question.


A qualified and experienced (at least 5, maybe 10 years) should asses the system. Here’s our rouge guide;


All systems;

(Inhibitor levels must be maintained with any filters cleaned).

Boilers must be serviced.


Checks for systems;

  1. Colour of heating system water (use Fernox test tool, do not use first water drawn off)

  2. pH level of heating system water

  3. Are radiators reaching surface temperature use an infrared thermometer, not by hand. (If not power flush, check pump performance and size)

  4. Age of radiators and heat exchanger (unless stainless steel) and pipework. The older the ferrous parts of the system are the more likely a flush and power flush will be necessary.

  5. Sealed/open vented. Open vented system more likely to oxidise so treat same as an older system and consider sealing the system.

  6. Magnetic check, if a small powerful magnet sticks to copper pipe the pipes need to be replaced (a thorough power flush is a minimum but not a long-term solution).

  7. Age and condition of heating circulating pumps. Some pumps should be changed as an addition.


Failing of 1 or 2 chemical flush required.

Failing of 1 or 2 and 3 Power flush required.

Older components of the system, magnetic flier required.



pH under 6 or over 8 (invalidates some warranties e.g. Worcester Bosch)

Filters always recommended for older systems (not always space) and these improve efficiency.

Boiler service always recommended, an aluminium heat exchanger may need cleaning (some brands should be cleaned annual, always refer to manufacturers instructions).


Only settle for a chemical clean when the heating engineer is satisfied that all the radiators reach approximate design temperature, this indicates good circulation, however if some (usually in a house ground floor) radiators are found to not reach design temperature then it is likely that there are significant deposits of sludge/debris (iron and/or aluminium oxides) in your heating system, then the preferred cleaning method should be a power flush. Pumps and other related components must be checked.


Inhibitor labelling should be used (inside boiler panel, or under boiler?)


Fernox sample lab test kits are available cost + one hour labour.




Example 1

Water clear

pH 6.5-7.5

All parts of system new, less than 10 years old

Radiators reaching the design surface temperature

no action  required.


Example 2

Water dirty.

pH 6.5-7.5

All radiators getting hot.

Boiler and radiators less than 20 years old.

Chemical flush and filter.


Example 3

Water dirty

pH neutral

All radiators getting hot.

Radiators over 40 years old.

Chemical flush and replace radiators.


Example 4

Water dirty

pH 8 or over (or under 6)

All radiators getting hot.

Radiators over 40 years old.

Power flush + replace radiators, magnetic filter recommended.


Example 5

Water dirty

pH 8 or over (or under 6)

Radiators not getting hot throughout

Radiators 10 years old

Power flush + magnetic filter


Power flush procedure;


Chemical Flush Procedure;


Commercial Flushing Procedure;







Gas Safe Reg no 305929

Company No. 07980305

VAT No. GB172932986

D-U-N-S Number: 21-827-8135


Primary Coverage;

NW1 Camden, Primrose Hill

NW2 Willesden Green Cricklewood, Childs Hill

NW3 Hampstead, Belsize

NW5 Kentish Town, Camden

NW6 West Hampstead, Kilburn, Queens Park

NW7 Mill HIll

NW8 St Johns Wood

NW10 Kensal Rise, Harlesden, Willesden

NW11 Golders Green Hampstead Garden Suburb

W9 Maida Vale

W10 North Kensington, Queens Park

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