So you're build your own waste oil heater, and having trouble keeping it to a steady temperature using a needle valve or tap. It wants to increase in temperature without you even touching anything, and sometimes even turns into a chernobyl nuclear reactor.
Why does it happen? Well it's simple, as oil warms up, oil flows faster into your heater, so if you walk away from it, your heater can get out of control very quickly. Because you can't see the increase of fuel entering the fire. This took us a few years to work out that the only way around this common problem with waste oil heating, was to use a timer and a pump to control that oil flow, and now it does.
There are a few rules regarding burning oil.
#1 If the heater is inside, keep the oil outside, or via versa, this well stop the oil from heating up, therefore making it more stable, just watch out for the sunshine even that will alter the flow rate. So best situation is heater outside, oil inside.
#2 Needle valves, brass wheel water valves don't control oil flow. No tap we have tried works all taps will flow faster when the oil temperature increase.
This tends to occurs more with the older drip type heaters than the fan forced heaters, however oil is oil and it can be tricky stuff to control.
We have been through those terrible frightening times with the drip fed heaters, when the heater cylinder and flue turns red-white hot inside the new home and at 1200c you start to think how the ceiling doesn't catch on fire, and you know there's nothing you can do, to slow it down, apart from turning off oil flow and letting it burn out, and closing all air inlets. Using the garden hose on very fine mist sort of cools it down but more turns your shed into a bloody sauna, don't let the water into the burning pot or the water will explode.
So our advice keep the heater outside and use hotwater to heat the home via radiators. Use a plumber to connect it up. You'll need a Ajax Valve and a open vent.
The only way is to pump it, to control the flow, this keeps the heater at a set temperature and very stable. This is the only option we have found that works. It's like a life jacket on a boat. You don't have to wear it, but one day it just may pay.
So with a waste oil heater controller, now controls the oil flow, whether the oil gets hot or cold, it never changes the amount sent to the heater. By doing this, it controls the upper temperature, and with the thermostat which controls the lower temperatures. Customers now find they can leave their heaters going all day, all night, with this controller and it never have to check the heater, giving them total peace of mind.
The thermostat now been added to the controller, should the heater or in our case, the water temperature to the radiator drop below 40c the thermostat cuts the oil flow off stopping the heater. The issue I have had with gravity fed heaters, should the flame ever get low or go out, the oil would continue to flow causing an oil spill until your oil container emptied out. This controller turns the oil flow off, fixing these issues and turns the heater into a very stable and safe heating option.