dwarf beans won't germinate

Sounds like you have a bad batch of seeds especially as you have germinated other bead seeds successfully. I have not had any problems with my seeds from a different company - almost 100% germination. Only difference is that I did not sow my beans until beginning of beginning of April as I think that they need a bit more heat.

mmm, thanks guys, I was also thinking a bad batch, except that I bought all my seeds from T&M this year and everything else has been great. I'll pick up some more from a different supplier and see what happens. 

T&M are usually pretty good about replacements.  If you bought the seeds from a garden centre, they will more than likely exchange them for you. 

Just a thought but is your greenhouse heated?  Dwarf beans are a bit more sensitive to cold than runners, so maybe a windowsill might give better results 

I had this problem last year, now I start (chit) all my large seeds in kitchen paper and a plastic container, they were placed in the kitchen window and had sprouted in 2 days, give this a try before buying new.

I have had some mixed results with bean seed germination.  Failure or patchy germination in pots root trainers or directly.  So I took to chitting and noting germination rates before sowing the chitted seeds in root trainers.  Germination/chitting success has varied between a totally unacceptable 50% for some dwarf beans and 80% for some climbing beans this year.  At least sowing these into root trainers you get 100% growing on.  I am not so concerned about the cost of the seed (although 50% germination is pushing it) it's more the wasted effort and the time lost.

What are other peoples germination rates with this method?

Update:

I planted two more trays 10 days or so ago, 1 tray in the greenhouse, 1 tray in the cold frame with the lid open. Nothing from the greenhouse ones but all those in the cold frame have germinated 

I'm guessing that it was just too darn hot in the greenhouse!