Miraco has a good little heater with built in thermostat as shown on page 17 of their catalog here. This is not too expensive and maybe you just want to disconnect the old Behlen heater, stick this one in the water under the float and plug it in. You can buy this heater at any place that sells the Mirafount waterers. just an idea. 

I would also suggest you buy the Miraco thermostatically controlled dangling cable line heater shown on the same page and dangle that down in the water line hole and get rid of that dang light bulb. You never known when that bulb will burn out and it is not needed all the time. Will prob just burn out on a cold night when you need it.  Good luck.

Jim at Dawn

edit: my main waterer is a Petersen concrete which I am very pleased with. I needed to add a couple smaller waterers to be able to split up my herd at times when a garden hose to a stock tank was just not the thing to do. So I put in a couple of these less expensive and easier to install (lighter!) plastic 3101 Mirafount units this summer and so far they seem to be working very well.I figure I can always run the cattle over to the concrete water if I have a problem but so far so good.

With all of them you need to keep lime from building up on the heater element and thermostat. I soaked my heater elements in a lime remover this fall and and they all work much better. Here is a picture of one of the Mirafount installations. We'll see how well it holds up.  It is supposed to get down to single digits (F = -14 C) tonight so we'll see how the heaters work. Should be OK from what I have seen so far. On Wisconsin football.

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