UV detectors work great but can "fail" unsafe, indicating flame, when there is none, when they get saturated. Hence the code requirements for flame detectors that run continuously to use a shutter-check mechanism that blanks out the UV from the flame and determines whether the UV tube stays on (failure mode) or turns off (OK). The applicable codes state that if the burner is not turned off at least once in a 24 period, then shutter check style flame detectors need to be used. Shutter check UVs are quite expensive $2-3,000.
An alternative is a pilot assembly with its own flame rod detection.
Look at Honeywell's Q179B, C or D Flame rectifier Gas pilot assemblies.
typical:
http://customer.honeywell.com/honeywell/ProductInfo.aspx/Q179B1042
The pilot assembly is a mechanical assembly, you'd still need a flame safeguard "flame switch" electronic unit that tells you whether you have flame or not, something like RM7823A1016 (115Vac),
http://customer.honeywell.com/honeywell/ProductInfo.aspx/RM7823A1016
with mounting subbase Q7800Axxxx,
http://customer.honeywell.com/honeywell/ProductInfo.aspx/Q7800A1005
a flame rod amplifier card, (just can't remember model number)
and an ignition transformer (can't recall a model #)
I always have an S7800A indicating display, because it
- saves a history of failures
- has a Modbus RTU (RS485) output
- moveable, can be moved from flame safeguard to flamesafeguard
http://customer.honeywell.com/honeywell/ProductInfo.aspx/S7800A1001
Dan