Hi my peugeot boxer 2007 2.2hdi oil light flashes exactly 28 times befor going off changed oil and filter no change. problem started after having new egr valve, new fuel pressure valve and new fuel pressure sensor fitted any ideas. many thanks

There's no air filter warning light - that's particulate filter (aka DPF or FAP).

http://www.servicing.peugeot.co.uk/diesel-particulate-filter/

Worn main and rod bearings on the crank shaft. This is what creates the oil pressure. When the get worn they start loosing pressure. Also when the oil gets hot, it gets thinner, causing more lose of pressure.

Check oil pressure with a gauge. The sender is electronic and could be the issue. Also oil filter could have a bad check valve. Change the oil filter, oil and sender. If the problem is still there you have worn engine bearings and major issues are coming your way.

Is the check engine light on all the time or it is it off?

I know same problem happening in another Peugeot was told he has a tubro problem but his check engine light is on all the time but accidentally it goes off sometimes for few days.

Do you see alot of heat/air or smoke coming out when you open the oil chamber?

Probably oil leakage going to a sensor?

Anything to do with the pistons seals?

Check to see if gas is getting into the oil which would raise the level. This can happen from flooding, i.e. a leaky injector dumping too much gas or possibly gas blowby past the piston rings and ending up in crankcase. If gas is in the oil most likely an injector is bad. Smell the oil and check to see if it smells like gas and or check viscosity of oil.. thin oil

fuel is leaking into the sump
if diesel it will be from the pump and if petrol will be leaking injector seals

Try reading the OBDII with a code reader and see what it is then erase codes and see if it stays off ,could be more than one circuit on this fuse so the fuse blowing has thrown the light on for whatever reason ,Also try disconnecting the battery just out of interest for a few minutes and reconnect it might go out if your lucky

The "Oil Change Reminder Light" has to be reset.

To reset the oil change reminder light with the accelerator pedal, turn the ignition switch to the ON position. Do not start engine. After turning the ignition ON, depress the accelerator pedal fully to the floor and let it up again 3 times within 5 seconds. The oil change reminder light should flash a few times to let you know that it is resetting. If it does not flash, turn the switch OFF and repeat the procedure. After it flashes, turn the ignition switch OFF. Then start the engine. The light should come on for a bulb check then go out and stay out.

Before driving again, check your oil level. It is not uncommon for Peugeot's to leak a little oil. Great cars in my opinion, but do leak a little oil. If all is ok, an oil change may be due with a manufacturer oil filter. Please let me know if you need anything else. I have a 205 shop manual if you need it. No charge!!

black smoke is not enough air or excessive fuel
if turbo , the turbo is not working and boosting, injector failure
incorrect fuel in system ( petrol instead of diesel)
water in fuel will damage injector tips