Pressure rising in Baxi combi boiler

[meems3434]

Hello, I was wondering if anyone could advise me about what's going on with our boiler. It's a Baxi 100HE combi boiler. Been in about 5 years and had a new PCB and was serviced a couple of months ago.
At some point since then some brown, gunky liquid has leaked out from some part of the boiler. Brown water marks over some things that were at the bottom of the cupboard the boiler is housed in. Not a huge amount and all completely dry now so hasn't happened in the last couple of days. This led me to look at the controls and the pressure gauge was showing low pressure (in the red section). No heating or hot water going at the time. I topped it up so it was just in the green (just below 1 bar on the scale). Only small amount but when the CH was put on the needle on the gauge moved round to over 3 bar. I turned it off quick(!) and it's now returned to just below 1 bar.
Am now sitting shivering and thinking it's probably not a good idea to put it back on until a heating engineer has looked at it. Would that be the right thing to do and does anyone have any advice as to what's gone wrong with it?
Thank you

 

[shorky]

sounds like an expansion problem, get your service engineer back, this should be checked at regular intervals and normally on a service. im not overly farmiliar with this paticular boiler but it could be an auto air vent leaking within the boiler(the brown stuff) needs to be checked by an rgi really, someone else on here will know this boiler far better than me though, it does seem like an expansion problem like i said.