The main considerations here, are age, value, and spares availability. The next thing is to identify the spares required to fix the item, find a supplier, and price. Don’t forget to add Post & Packing, then add VAT on to the lot. Then go to a catalogue, like Argos, or on the web, and price up the cost of a replacement.
Obviously a major appliance like a washing machine or dishwasher may well still be worth fixing, even if you need a couple of hoses, and a pump for example, and it is not over 10 years old. Over that age, and spares become increasingly diffIcult to source. Having said that, I did keep our AEG LAVAMAT REGINA washing machine going for 26 years!
Bosch and Miele fridges for example, will be well worth replacing doors, handles, door seals, and it is usually easy to get replacement food trays if you break one. See the useful links section for appliance spares. The actual motor and cooling elements on fridges and freezers are sealed systems, so it is best to cover these on an insurance policy, and call in a professional if yours does not work at all
Vacuum cleaners are generally quite easy to get spares for, especially the well-known makes like DYSON and HOOVER. Obviously if you need several expensive parts, you will need to asses your situation. Bear in mind though, that DYSON have a 2 year parts guarantee, except for the belt and filters, and the tools. So, if your motor, or hose fails, you should be able to get this replaced, provided you registered it. The hose just clips in, but you will need to be fairly competent with appliances to replace the motor, some screws are hard to locate and see (depends on model). Many models use hard to reach TORX screws to remove the casework to replace the motor.
If we look at something smaller, like a kettle or toaster, then these are rarely worth fixing, unless it is a special one, that is relatively new, and it is something easy to obtain, like an element. I know that Russell Hobbs still make the “classic” chrome kettle, and you can probably still get the element (for the K2 and the K3, but probably not the older K1, at around £13, from http://www.heatingelementcompany.co.uk ). However, the older type will need a special hollow-tube screwdriver to remove the earth tab, and the element plus P&P and vat will almost cover the cost of a low-end new jug kettle. Note that the concealed element kettles do not generally have replaceable elements.
FANS: These are rarely worth fixing, but certainly worth MAINTAINING. What I mean by this,is ensuring that the mesh blade cover is removed from time to time, and the accumulated dust vacuumed off (or brushed with soapy water and dried). The centre plastic screw is usually left-hand thread, so it is clockwise to unscrew it, and remove the blade for cleaning. With the blade removed, put a couple of drops of light oil on the lowest part of the spindle. Spin it back and forth a few times to distribute the oil into the bearing. What often happens with these sort of pedestal or desk fans, is that the accumulated dust finds its way into the front bearing spindle, and will eventually cause the fan to slow down.As this gets worse, if not corrected, you will find that the fan will not start up on the slowest setting. That is a good test to see if you need to clean and oil it.
SHAVERS: These can be surprisingly expensive to replace these days, especially the ones with fancy features, like a cleaning station. If yours is a well-known make, like BRAUN or PHILIPS, then you should be OK for some spares, such as foils, cutter blades and rotary blades, for around £10 (try OLYMPIC SHAVER CENTRE). If yours is a mains/battery (re-chargable), and the battery will not hold its charge for long, then you MIGHT be able to get it fixed if the battery is based on one or more of the standard sized (AA) solder-tagged NiCad batteries. MAPLIN sell a NiCad AA tagged battery (VN39N, at £2.49), and a longer lasting NiMH on (VN19V) for £3.99. They sell higher capacity tagged ones too, if yours needs a C size.You will find the biggest problem is getting the shaver apart (very small Philips screws), and there may be some plastic “latches” to defeat. Use a piece of double-sided tape to hold the new battery firmly on to the circuit board, so that it does not detatch if dropped, then solder in place.