Expansion tank`s part in flushing the system

[puppy]

I had a new Baxi Solo 3PFL boiler installed last week and on testing the central heating yesterday I found that the expansion tank started to overflow. I went into the loft to have a look and could see that the water in the expansion tank was filthy, with sludge stuck to the sides and floating on top. The installers said the system would be flushed before and after the installation so if they did flush it properly could the expansion tank still be in this filthy condition?
The installation firm is well known in the South East and give a full guatantee for twelve months. The work was also inspected by a company inspector during and after the installation and he passed it fit for use.
The expansion tank is sited in a hard to access part of the loft and I`m wondering if the fitter and inspector bothered to check it as it meant squeezing through a narrow gap to get close to it.

 

[djbunny]

When flushing a system it is good practice to wash out feed and expasion tank, but sounds like it was not done. You will find that the level in the tank is too high so as the system heats the water expands, the level in the tank rises and overflows. as a rule of thumb you should have about 4-5 inches of water in the tank when system is cold.