The condenser ( the thing you pull out from the bottom, its not a filter BTW ) needs to be kept clean, if you lie down on the floor and reach right back into the condenser housing you may be able to feel a build up of gunge. Pull as much out as you can.
The best way to clean the condenser is with a hose pipe or pressure hose in the garden.
The most common cause of no heat is failed thermostats located above the heater at the back.
As always, plug out before opening up.
Part number of stats is C00095566 or 1701583.STATS
NB. Moved you to correct forum.
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