Potterton Puma 80 Losing pressure?

It's not a good thing to keep topping the boiler up too frequently. It can cause sediment build up in the boiler and radiators.
As for the air vent that applies to open -flued appliances(ones that take the air for combustion from the room they are in).
I've not seen a puma 80 that is open-flued. Most modern combi's are fan-flued and don't need air vent's unless they are fitted in a cupboard or compartment.
If your boiler flue bends straight off the top of the boiler and goes out through the wall, the chances are that its got a fan and doesn't need an air vent.
If you are in doubt get the landlord to get someone to confirm this for you.
IT'S HIS RESPONSIBILITY IN LAW TO MAKE SURE THAT THE PROPERTY HAS A CURRENT GAS SAFETY CERTIFICATE WHICH HAS TO BE RENEWED EVERY 12 MONTHS. THERE ARE NO EXCEPTIONS.
There should be a copy of the inspection certificate in the premesis along with a copy of the installation and service instructions for the gas appliances.
Anyone he sends round should show you their CORGI membership card. It's a plastic card with their picture on it and the expiry date. Again there are no exceptions. On the reverse of the card will be a list of the types of work they are qualified to do.
Hope this helps..

T.h.s
May 2007