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This short guide is an edited extract from MAINSTEAM MODELS "The Complete guide to Miniature Steam" which is now available on CDROM or Internet download . It is written with the beginner in mind and covers many essential principles for sucessful running of miniature steam engines, locomotives, traction engines & steam boats.

The ever popular centre flue type model steam boilers work by having a central tube through the boiler to the chimney, this tube has several cross water tubes in it which allows a greater surface area to be heated. The blowlamp flame heats both the centre tube & the water in the cross tubes to boil the water.

The usual problem with all gas fired centre flue boilers is the heat source & especially the lack of constant high gas pressure. Blowlamps do not take kindly to blowing into a centre flue. With the blowlamp type of burner, the distance from the burner to the fire hole has to be experimented with. It is a good idea to have the blowlamp about 1/2 an inch outside the centre flue so that the point of the blowlamp flame is on the first water tubes.

The universal problem with all gas fired boilers, is that the gas canister soon "chills", owing to the rapid evaporation of the liquid gas inside the canister. This then causes a drop in pressure & less heat is obtained from the burner. Do not use propane as the pressure of propane is too high & far too dangerous.
I sometimes use a small piece of ceramic gas fire element inside the centre flue, up against the first cross tube. This has two advantages, from the blast of the burner, the ceramic block glows bright red so will re-light the burner if it blows out, also it protects the first cross tube from the fierceness of the blast.


Please be aware that all parts of the boiler get EXTREMELY HOT when running - ESPECIALLY THE CHIMNEY - It is very easy to accidentally touch the chimney when adjusting the blower. (I speak from experience - several times!)
Lighting the burner should be carried out by holding a match or cigarette lighter near the burner head - then slowly opening the gas valve on the canister.  Lighting from cold via the chimney is not recommended.Initially the gas valve only needs to "cracked" open slightly as the canister pressure is higher, until it cools off a bit, then the gas valve can be opened up a bit more to suit.
I hope this helps anyone out there to keep the heat up!

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