The boiler is leaking a sticky brown liquid out the top and there is a steady drip coming out the bottom of the boiler as well, Now i have to turn the water supply off in order to stop the leaking but there is still water in the actual boiler system???
If the leak is from the top of the Boiler, you almost certainly have a leaking Automatic Air Vent(AAV). The dirty water indicates that you have Sludge in your system, which prevents the AAV stopping the water when it has let air out. You will need a new AAV, but also it is advisable to have the system flushed to remove Sludge, otherwise the problem will reoccurr. It is advisable to turn the boiler off at the main electrical switch not use the boiler until you have had the repairs carried out, as apart from the safety implications of water in electrics, the water could damage the Printed Circuit Board, which would make the repairs much more expensive.
Check the cold water pipe, they may have turned the hot water off by using the isolator on the cold inlet of the boiler, no need to do this as the main stop tap would have the same effect, and the wash mac taps isolate washing machine supply anyway. If not the valve, I would say either the heat exchanger has sprung a leak, or the auto air vent is passing, the pressure will drop on the gauge if this is so. Neither are likely to have been caused by the washer installer whether he was dodgy or not.
The brown is rust.leak at top is prob over pressure valve.Bottom..if not coming from pipes that need replacing better have boiler checked.if pin holes from rust in bottom it is no longer safe under pressure.pipes and joints can be replaced or fixed if loose.A boiler that leaks from too much rust is potentially dangerous.Get a licensed plumber who has boiler experience to look at it.
