OK I called the original fitter back to service the boiler and sort the repair.
he said that the water isn't oily and sludgy but just black because of a chemical reaction. He recommended that the whole system be flushed out. As he was paid to do that 3 years ago when he fitted the boiler I...
The boiler was installed only about 3 years ago and cost a lot of money. We had a catalogue of disasters. The engineer left his apprentice to flush the system and fit a new radiator in the lounge. We ended up with a soaking wet carpet under the newly- installed radiator and dirty water all over...