FY7 is the Fleetwood area... so taking
Houses for sale in Fleetwood, Lancashire, FY7 6FQ - Harbour Village as an example postcode... give a prediction like this
Coverage Checker - Detailed View
Have you ever connected the aerial to one outlet direct (i.e. no amplifier at all)? If no do give it a go - especially the next time you get problems... it may even be possible to passively split the signal to two receivers if the levels are strong enough. Assuming you do need an amplifier, though: if the 4-way amplifier has a variable gain control try it lower as well as higher when you next have problems... too much signal can be as bad as too little. Ideally any unused outlets should have a 75-ohm termination on them. Therefore it is a good idea to go over all the connections and plugs/socket with a fine tooth comb to ensure there are no dodgy joints, crushed or damaged cables and loose joints.
You are likely to have a Wolsey amplifier as well as the power unit... It is possible that the amplifier is over-heating or the power supply brick also, either of which could add noise and other 'nasties' that upset the signal - but both would need opening up to see if they had problem with the internal component, or use the substitution method to eliminate them (i.e. another psu and/or amplifier). Masthead amps are usually mounted outside and, in direct sunlight, will get hotter than any loft should get, so are
usually designed to cope with extremes of temperature with no issues. (The psu is a different matter, of course). Cables and connections can also expand and contract with heat and in unusual cases solid wires can fracture or the connections work loose - this can be enough to give very odd frequency dependent problems that are intermittent.
BTW, there's no such thing as a 'standard' loft aerial... have a look at
Aerials, TV Aerial and Digital Aerial and see which of the ones pictured is like to one you have fitted.
Loft and indoor aerial installations for TV, FM and DAB and Television Aerial Boosters / Amplifiers, Splitters, Diplexers & Triplexers also make useful reading.
It's quite possible, of course, that the aerial need relocating within the loft space to equalise the signal levels: higher/lower, crabbed left/right and nearer/further from the transmitter while maintaining the same pointing direction... the problem is that then the issue may change to affect one of the other frequencies. (A good aerial installer would use a meter - or better a spectrum analyser display - to ensure all the frequencies are received equally strongly).
