I get all my spares from Heating World of Spares.
I only carry one type of flexi hose, the one HWOS calls Long01. If I find a different one on, I change the fittings to suit the Long01 hose. I don't see the point of carrying loads of different ended hoses. In all the time I have been doing boilers I have only ever come across 2 boilers which this hose did not fit and needed an elbow at the opposite end to the pump because of shortage of space.
Combustion analyser and printer (I scrounge till rolls from my local pub for it as one lasts ages and I'd never get through a full box of them)
Smoke pump and papers
Pressure and vacuum gauge set
Fuel priming pump (one from an automotive supplier is adequate)
Bearing puller for removing fans and motor bearings - I find this is the best
BERGEN Prof Heavy Duty Bearing Puller 'B' Type 24-55mm on eBay (end time 06-Mar-11 19:11:56 GMT)
couple of pairs of 6202RS bearings (from Ebay - bur only get good branded ones, SKF, NTC etc) You'll know when the bearings are worn as the burner motor will make a rumbling / whining noise.
Pump drive couplings from HWOS
Selection of nipples, elbows, couplings etc from the fittings page at HWOS
Pipe flaring tool off Ebay (no point in getting an expensive one as you don't need it that often)
OFTEC forms - servicing and commissioning, oil storage risk assessment, installation
One of those magnetic pickup tools which looks like a radio aerial with a magnet on the end
1/4" ratchet set and extension pieces (get a good quality set such as Britool)
T handle long reach hex set
Screwdriver handled socket driver
glass rope and glass rope adhesive
STAG B jointing compound (prefer this to Heldite another post mentioned as Heldite is awful to get off your fingers etc)
PTFE tape (normal and gas tite (yellow spool))
roll of 10mm copper pipe (white plastic coated) and roll of uncoated
spare 3m 65 degreesC Teddington KBB fire valve (you can get more of different sizes as you go on)
GOOD selection of nozzles (from 0.50 to 1.0 USgall/h - larger ones you won't come across often and can order them as required. Get just kerosene ones to begin with (ES & EH). Some boilers will specify W nozzles you can buy as and when on next day delivery)
PLENTY of 10mm brass inserts for copper pipe (HWOS do packs of 100)
Selection of steel nuts for when you loose some behind the back of a boiler so you don't need to spend ages looking for them.
Heat proof gloves for dismantling hot combustion chambers (I use welders gloves)
disposable vinyl gloves like the dentist uses
Barrier cream
Beaded hand cleaner
Hand cream
One of each of the cleaning brushes that HWOS do
Container to put waste oil into when cleaning out filters etc
Spare filter elements (just get the two Crossland ones to begin with)
Vacuum cleaner and spare bags (I use an old VAX cleaner but any will do)
Dust sheets
Kneepads (a MUST HAVE!)
Tub of fire cement
Tube of heatseal silicone and gun
Multimeter
Spare 3 amp fuses (a lot of boilers just have 13 amp fitted so should be changed)
Boiler manufacturers literature to show to customers when persuading them to change to a new boiler.
long 18/19mm drill but for drillling holes through walls for oil lines / fire valve capillaries
Parts organiser box for all your fittings
Nozzle box
Set of flat, pozi and philips screwdrivers
8mm copper pipe and fittings for where you have a tank lower than the boiler (lot of people post problems on here caused by too large diameter pipe where tank is lower than boiler - always follow the table in the OFTEC book!)
Set of combi spanners from 6mm up to 17mm and inlcuding ALL the inbetween sizes
Scraper (paint scraper)
Selection of metric machine screws (probably be able to get an assortment box from Toolstation these days)
Torch (head torches are useful)
Tape measure
Circlip pliers
pump pliers
Standard pliers/nippers
Set of adjustable spanners
Beware of buying analysers not working. Sometimes they can be very expensive to fix.
If they are just out of calibration it is simple to sort. Don't buy anything too old. You want something which comes with a printer too!