Tvheadend

Assuming you are using a universal LNB when you have two inputs connected to the same feed they will only be able to tune to the same group of channels.

To access both polarisations and bands (Horizontal and Vertical; Low band and High Band) an LNB will operate in four discrete modes - this means that for PVR applications you ideally need a feed per tuner - and that a single LNB can only provide access to around 1/4 of the available channels at once.

If you use a passive splitter you will find that one of the following happens
1) A tuner connected to one output always wins
2) 22Hz switching being on (i.e. Highband) always wins, polarisation from one output always wins
3) Horizontal polarisation being selected always wins, 22Hz switch from one output always wins
4) Horizontal polarisation and High Band win
5) When output one is active that wins, and output two gets nothing

1, 4, and 5 are the most likely outcomes

Assuming you are using Astra at 19.2'E try tuning to

11.479V - TV Monde on tuner 1
11.509V - Montanggne TV on tuner 2

If any of 1 - 4 are yours then both of these should be viewable.

Basically you can tune to one, and only one, of the following four groups of channels at once:-
Lo Band Vertical - 10.700 - 11.700 Vert - 22Hz OFF, 13V
Lo Band Horizontal - 10.700 - 11.700 Horiz - 22Hz OFF, 18V
Hi Band Vertical - 11.700 - 12.750 Vert - 22Hz ON, 13V
Hi Band Horizontal - 11.700 - 12.750 Horiz - 22Hz ON, 18V

For a PVR application this would obviously be rather unpredictable!
(It would be neat if you could specify in TV Headend "Tuner B can only tune to the same band / pol as Tuner A" to allow the flexibility in recording when you have a single feed while leaving it semi-predictable - i.e. a recording doesn't die half way through)

Sorry I must not have provided enough information. In New Zealand we only receive from three transponders, all Horz with 22Hz off, I have used this configuration on Windows Media Center in the past without issue. I believe I have had it working on tvheadend too in the past but cant work out why it does not work now.

Have you checked the obvious?

Namely remove the splitter from the equation - connect the feed directly to card 1, check that it works. Then connect to card 2 and check that works? You post implies that you have only tried removing a card rather than the splitter.

Assuming that works add the splitter in and check one leg on each card in turn and so on.

If that works it could be an issue with the cables - when I mis-wired the cable (one of the outer strands was touching the inner one) it caused the LNB to switch off when I connected a receiver to that cable.

Another thing which is ringing a bell from years ago - have you tried leaving a gap between the two cards in the tuner (e.g. have one card in slot one, something else or nothing in the next slot, and then the second card in PCI slot 3).

Got it sorted, replaced the dish and it all worked straight away!!!