I read off your description and my husband says that it could be one of many things. He said the smell of gas immediately makes him say "talk to a professional".
Yeah, that was my thought too!
He is now asking what kind of heating system you have. He said our doesn't have a pressure gauge as it is an open system (not a combi boiler). Apparently only closed systems have pressure gauges. He's saying, "it could be the pressure." Helpful, eh? LOL. 
I have a boiler in a cupboard downstairs in the kitchen (it's a Baxi Solo 2 40PF), and a hot water cylinder in the airing cupboard upstairs (not sure if there's anything in the attic as I can't easily get up there). I think the boiler is about 10 years old now, but I don't really have much experience with what can go wrong with them, as I'd always rented before.
I will admit to not having had the boiler serviced since I bought the house 2 years ago... it totally slipped my mind as something that needed to be done.
Hoping it's a fairly easy fix, because I'd rather not have to buy a whole new boiler (I'm supposed to be using my savings for a new car sometime soon).
Worse case scenario, hop on amazon and get one of those electric heaters to hold you over if it gets worse.
I have a plug-in one already (
like this one), which is keeping the living room warm... it's just freezing when I go into the other rooms

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