Hi there, we have had a harmony 5 (EFEL) 5kw small room heater in the sitting room for about 10 years now. We found it a bit troublesome for a number of years at the beginning, would not burn clean and calling out various professionals did not seem to get to the bottom of the problems. However, we finally figured out how to get the best from the unit and are so happy with it, I'm thinking of fitting a 2nd one in another part of the house that could do with the constant flow of silent, effortless, low-cost heat.
Here's the experience we have gained with this unit over the years:-
Apart from making sure that it's installed correctly, especially that the flue is lined properly, the main two things with getting these devices running really efficient & trouble free are:-
1. They need a good fuel flow, when the device is burning correct temp. you have little blue flames 'dancing' in the pot, even when the wind is howling there's no issue. When you starve it of fuel, e.g. when you turn it off, you see yellow flames & smoke as the unit goes out. If the unit is getting starved of fuel during normal operation (i.e. you haven't deliberately turned it off), it will begin to burn yellow flames. This is usually caused by some problem with fuel flow. 1st port of call would be to give the decoking lever a good pull & twisting action to move the gunk that can build up (a coal/coke like substance that is really hard to shift). using the de-coking lever is sometimes not enough and you should let the unit cool down fully and remove the bits inside in the pot carefully (if red/brown colour on the metal = good, if black / sooty = bad). The inside of the pot will need a good scraping out with a flat-head screwdriver, use a light & small mirror to see inside the pot, especially checking around the spot where the oil comes in for 'gunk' and the coal-like stuff you have to remove. have the vacuum cleaner on hand to remove the stuff you scrape out. lay out old newspapers around the stove & put on disposable gloves for the operation, you will get very dirty otherwise. Sounds like a lot of work, but I only need to do this operation a few times a season, at the start and 6-8 weeks into the winter. It's worth the effort as the unit will burn really clean after this and the glass will stay perfectly clean for weeks. The trick is to get the bottom of the pot very clean so the fuel can spread out evenly, that's how the vapor burns evenly up through the pot. if the fuel sits in one end of the pot, it won't burn correctly.
2. these units like to be left on 24x7, we don't turn the unit off unless we are going away for a weekend, so it will typically run for 6-8 weeks at a time non-stop from November to spring. Have a smoke detector in the room and make sure a fire-valve* was fitted (little cylinder with copper wire running to a probe).
Back in the early days we used to turn off the unit overnight, re-starting in the am, it would get clogged with the gunk very quickly. one of the guys we had out to look at it did say that they run better left on 24x7 and that is good advice, there's no trouble from the unit once it's cleaned and then just left to run.
*One little detail to check on the fire valve is to know when it's off or on. there is a little button on the unit, on ours in is on and out is off...kind of the opposite to what you would expect!
Hopefully that is some useful tips for you.