Welcome to GoY, your rhododendron could be pot bound, underfed, in full sun... Could you add a photo to your question please.

How long's it been in the same pot?

Are the flower buds turning brown and crispy? If so, you should try to pick them all off and bin or burn them, don't compost them. My dwarf Rhodie had this and it has been cured by picking off dead buds and also spraying with a fungicide after new buds have formed (in late summer). Also, a feed with ericaceous food would be good. You can buy pellets or a powder to mix up and water on.

Thats interesting Volunteer. I have had the same problem with an azalea these past two years and I assumed it was frost damage as there were some flowers lower down on the bush. What do you think is causing the problem then?

It's probably some kind of fungal infection. Mine is flowering well this year, but it's been quite a long haul to get it clean. Fed and mulched it well last year.

Which fungicide would you recommend?