Help with tomato seeds.

My first year growing tomatoes from seed, and i already seem to have a problem.
i decided to grow
Marmande,
Moneymaker,
Tigerella,
and Black krim.
All the others have germinated, quite happily on my windowsill, and are now starting to show there first sets of proper leaves, but the krims arent doing anything, i ve treated them exactly the same, and have now gone through some 40 seeds to only 1 showing plant.
i'm using a good seeding compost, theyre warm and in a well lit window near the radiator for warmth.
Can anyone suggest what i may be doing wrong.
thanks

 

Some varieties are simply slower than others to germinate. Also some require a bit more warmth than others to germinate. It is a good idea to allow the temperature to drop at night, this can stimulate germination.

 

I got them from a company called Premier Seeds Direct. I'm going to give it another 7/10 days, then just order them as plugs, i only want 3.

 

As per JWK above, I've had 3 lots of seeds from Premier Seeds Direct (Amazon itself now stock them which is useful for making Amazon orders up to £10.) I've been very pleased and they seem like decent people, but bad batches do happen.

 

I got in touch with them, the reply i got was speedy and very polite, they offered me a refund and a new set of seeds. I told them that i didn't want a refund, but another lot of seeds would be appreciated. Next thing i know moneys back in the bank and an email of despatch was sent me.
After service like that, they've made me a new return customer.

 

I'm glad they sorted it for you. I've used Premier Seeds and they have always been very good.