I bleed 1/2 litre from radiator into a jug, frothy bubbles on the surface of the water, does that indicate air bubbles trapped in the water or is that normal ?

Also the water is clear but slight brownish tint, is that to be expected or should the water be crystal clear since it has recently be drained and refilled ?


Short answers:

  1. Condition is likely normal.
  2. Water does not need to be clear.


On the color - Despite being refilled with clean water, rust/sediment will remain within your system and radiators - causing the water to take on that color. Unless there is a reason to drain the system, introduction of excessive clean water will speed system corrosion due to the dissolved oxygen brought in with fresh water. In a closed system, old water is 'like fine wine'.

On the bubbles - If you let a sample sit exposed, do the bubbles disappear? If no, this suggests that they are caused by a chemical (other than water) that was added to / remain within the system (ie. antifreeze, corrosion inhibitor). If the bubbles disappear over time and do not remain on the sides of the container, this is the behavior expected of water used in radiant heating systems. If you boil the same sample of water on a stove top (not microwave!) and similar bubbles form, this also points to a chemical treatment in your system. Have you had work done on the system recently, but did not add a chemical additive? If so, the frothing may be caused by cutting oils introduced into the system. If the sample boils and settles like normal water - your frothy bubbles are normal and created during the bleeding process.

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  • Thankyou I think you a right, the system has recently been refilled and corrosion inhibititor added – Paul Taylor Dec 7 '17 at 9:08

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