OK - I got blower assembly apart, and the motor is difficult to turn. In addition the exhaust tubes were plugged with wasp nests and there is alot of rust coming out the exhaust tubes of the combustion chamber. With a replacement motor at $290, and then not sure if the control board, gas valve and burners are still workings, I'm wondering if there is a direct replacement on the market today for the DNV-40?

They no longer have a direct replacement for this unit. I have heard there may be a company trying to buy the rights to make these units again but we won't know until some time this spring.
When new they were selling for $1568.00

There is a similar unit to the Dynavent heater made by Cozy...the model number is WOW403 and you can see more information at wwwcozyheaters.com

Proflame - Thanks for the response. I didn't realize the unit was so expensive, so I will continue to take my unit apart to see what else I can find wrong. With the unit on a bench (not coneected to a gas line) and the blower fan not working, what can I do to check if the circuit board and gas valve are working?

You can bypass the sail switch by connecting the two wire together. This will tell the unit the blower is working and let the glowbar ignite.

After the glow bar ignites and glows orange the board will then engage the gas valve with 24 volts ac currect...you will hear a click when the valve opens.

If this will all happen then you are probably going to be ok with the board.

Proflame - Looks like everything is working except the motor, so i'll be ordering one next week - Thanks for your help getting me through the check-out!