starting issues

Hi ive got a series three with a 2.5 diesel engine . Been having starting troubles so i tested the output from the alternator and once engine running goes up to about 13.9 volts also had battery checked which was faulty so had it replaced under warrenty but still the engine takes a life time to fire up and someimes battery goes flat before she fires up. Someone suggested testing / cleaning glow plugs and thoughts / advice please would begreat.

Is it every time you go to start it or just when it has not been used for awhile?
2.5 is parallel glow plugs take wires off and touch a 12V supply to each one in turn should get similiar spark any that don't spark are open circuit.
Once its running remove the rocker cover vent is the engine breathing heavy?
If breathing heavy head gasket might of gone , diesel needs good compression to make it ignite.
If no breathing and only happens when been standing awhile check diesel fuel lines as air can get into them and make starting difficult.

Im betting on glow plugs being a factor. Mine takes ages to start unless I use glow plugs for about 20 seconds, fires up first time then. Is it spinning over fast or slow? If slow, the main cable from battery to starter could be corroded

Its been starting up fine only got mot on her couple of weeks ago but was having battery issues put new battery on last night and it started after a while now it wont fire up at all been trying for jalf an hour now even got jump leads on from other car. When running she seems fine

Any diesel leaks? Could be air in the system possibly.

Also, is the fuel solenoid working? I had the fuel solenoid on the pump fail on me a few weeks ago where it connected to my switch, engine cut out and wouldnt start until I bypassed the feed

Will check out air in system first and slowly work through the possible causes hopefully can finish work early this week and spend some evenings in the garage. At the moment all its doing is giving the wife more ammunition about getting rid of the ole girl.

crack open an injector pipe and see if you're getting fuel up there

if no fuel it's time to check the solenoid is getting electricity

just because it's getting electricity doesn't mean the solenoid hasn't died (infrequently happens) and refuses to lift the stop plunger, this can be checked by removing the solenoid and pulling the plunger and little spring out, replace the solenoid if it then starts you'll then have to stall the engine

air leaks before the lift pump can give starting problems as well as it'll suck air up easier than fuel

as already said, check your heater plugs are working first though