Diesel Heater Servicing Guide
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This website was written for owners of direct fired and indirect fired diesel heaters. These heaters can be fickle machines and require more regular servicing than most types of heaters. On this site we're going to look at some suggested servicing operations and the intervals at which they should be done. If however the heater isn't running well on these intervals, then the gaps should be reduced - dirty fuel or particle in the air (eg. paint or dust.) Then all servicing times will have to be reduced considerably.

* If possible when servicing or repairing a diesel heater, refer to the instruction manual or handbook before starting. Sometimes these have invaluable setup information or troubleshooting tips specific to the heater. If you buy a heater, look after the book.

1. Basic Service - Filter Bowl Clean.

The most common service task on these heaters is to clean the filter bowl. I would suggest doing this at every 100 hours if running on red diesel, possibly less if running on road diesel or kerosene. The process of removal is simple, simply unscrew the plastic bowl, then carefully remove the metal filter inside - taking care not to lose the rubber seals. These can look different, but work the same way.

If the filter doesn't look anything like the one below on the right ->

But looks more like the one below on the left :-

Diesel Heater Fuel Filter - Disposable Diesel Heater Fuel Filter - Cleanable

You have a non-cleanable disposable filter and these can't be cleaned. If have the non-cleanable type, then a new one should be ordered when it is too blocked. These should last a little longer between changes, and can sometimes be cleaned a little by blowing compressed air back through the filter, this will only ever give a few hours use though and a new one should be sought as soon as possible.

If you have the cleanable type, keep the rubber seals safe (There should be three, one small rubber washer that sits atop the filter, one O-ring that sits in the metal cap of the filter bowl and one stubby washer that sits in the bowl. If any of these go missing or get damaged it will seriously affect the heater. The O-ring from the cap going missing will stop the heater firing, as it will suck air in through the gap. The other two going missing will mean the fuel is no longer being filtered and the pump filter will get clogged up. If you lose these then should either order a new filter kit or new seal kit .

Having removed the metal filter, use compressed air to blow any debris off the outside of the mesh, if it's stubborn or sticking then a soft brush such as an old toothbrush can be gently rubbed on the outside to clear the gunk off. Once the outside of the filter is clean, you need to address the inside. If you take a clean filter and hold it to a bright light and look through it you should be able to see the remaining dirt on the inside. If you can't see any light through the filter then it is very clogged. Cleaning the inside is harder than the outside, if you can get a small brush that fits inside then use that - if not, then it's continuous compressed air work. If the grime is proving stubborn, soaking the filter in clean diesel or kerosene can soften the dirt up for removal.

2. Intermediate service - pump filter clean.

Every 200 hours it's worth checking the pump filter. Some cheaper pumps may not have a filter, particularly the electric fuel pumps. However if it's a fairly standard Danfoss or Suntec fuel pump which looks like the one below there is a filter which can be clogged:-

Diesel Heater Pump

This fuel pump fits on the opposite side of the motor to the fan, and has a feed and a return on the bottom, and a sender on the side. If for any reason you have to disconnect the pipes, make sure the feed runs through the filter.

To remove the filter, use an allen key to unscrew the disk on top of the pump as seen above. The white plastic filter should come out as you pull the metal cap out. If the filter is old, worn or particularly gunked up - then it may get stuck inside. If this is the case it's a matter of persevering with terminal screw drivers, long nose pliers and anything you can wedge in to firk it out. The filter should look something like this:-

The O- ring tends to stay on the metal cap.

Diesel Heater - Internal Pump Filter

When removing this filter, take care not to lose the plastic insert that goes in the middle. It won't filter if that part is lost.

3. Full Service / Major overhaul.

Once a year, every 1000 hours, or if a heater is not working properly - it's worth giving these heaters a major overhaul. As well as performing the above two operations, you should also:-

3.1 Remove and clean the burner head or blast tube.

If you look at this image:-

Diesel Heater Combustion Head

The two black plugs are the HT leads that join the electrodes to the transformer - unplug them, they don't need to go back in the right order. Some heaters only have one electrode. The single black plastic plug beneath these is the photocell, pull it out and put it to one side.

When you unscrew the fuel pipe from the nozzle, take care not to kink the fuel pipe, some heaters have a rigid steel fuel pipe, others have a copper pipe. If possible replace the copper with a steel rigid fuel pipe. When replacing this - take care not to overtighten, particularly on a copper pipe as the olive will cut through the pipe causing a leak.

Once the HT leads, photocell and fuel pipe are disconnected - you can remove the blast tube by unscrewing the four self-tappers at each corner of the square plate holding it onto the combustion chamber. Alternatively it might be easier to remove the burner assembly first - in this case by unscrewing two bolts on the top and bottom of the assembly.

If you get the burner assembly out and it looks like this:-

Diesel Heater - Dirty Nozzle

You have some work to do!

It's surprising this heater is still working at all!

What has happened here, is the fan has sucked particle in at the back - dust or paint particles, then these have melted onto the end of the nozzle. Eventually the nozzle would be blocked and the electrodes would be glued to the end of the nozzle. Try to clean the nozzle gently. Take care not to scratch the nozzle, particularly around the pin head, or rub grime into the pin head as this can block the nozzle or alter the spray pattern. Clean the electrodes too - preferably with some soft wire wool, try to get them shiny so they can make a good contact. Try to avoild loosening or moving the electrodes as these are set at a very carfully designed distane and angle for optimum performance and without manufacturers service book it may be difficult to get them right afterwards. It's good practice to change the nozzle for a new one as part of a major service. Always keep the old ones if the heater seemed to be running okay though - they might get you up and running if you get a blockage mid-season!

Again avoid moving the electrodes, if like some the electrodes are only fittable in a fixed position this isn't so much of an issue. If the electrodes are broken or excessively worn - change one at a time so you can copy the position of the existing electrode to the new one.

At the back of the burner assembly there should be either a metal plate with holes in or adjustable flaps as shown here:-

Diesel Heater Combustion Head Diesel heater Air Flap

In this example, the heater has been sucking in particle and it has got stuck on the air flap, restricting the air flow to the chamber slightly. If left unchecked this would eventually alter the air/fuel ratio and cause the heater to burn incorrectly. In the example on the right we have a different type of air-flap common on Master heaters and Spitwater/Heat Star heaters. On these the air flow is set by loosening the big jubilee clip and moving it to allow more or less air into the chamber. Without the manufacturers specification on how these should be set - they are best left alone. They do need to be kept clean though, as gunk will eventually build up and cause the heater to burn too rich (Not enough air).

Once the nozzle, electrodes, photocell and air flap is clean and serviceable we need to turn our attention to the opposite side of the blast tube. From the back this looks like this:-

Diesel Heater Turbo Disc

This side is usually clean, and should be cleaned if it isn't. We need to remove the tube and make sure the other side is clean as shown though:-

Diesel Heater Turbo Disc

This part has to be kept clean to ensure the flame sticks to the disk and the burn gets a nice 'swirl' to it. If it gets too gunked up - the flame can blow itself out and you end up with intermittant firing.

Once the blast tube is completely cleaned, the next step is to clean out the combustion chamber.

Referring to indirect heaters:- If after removing the tube you can get your hand into the chamber a rag or a soft wire brush can be used to clean the main chamber. If the chamber has been running badly for a long time then it may be badly sooted up and the only way to clean between the baffles and channels is to put gravel in, shake the entire chamber about, then empty the gravel - then replace with clean gravel and keep repeating. A little clean diesel into the chamber may soften up soot, a drastic measure might be to cut the chamber open to clean it out properly: obviously this presents the issue of welding stainless steel back together again - not something to be taken lightly!

If a heater isn't running right, particularly in an indirect - take action immediately, a clogged up combustion chamber can write a heater off!

Referring to direct heaters:- With direct heaters, it's still a good idea to clean out the chamber, but perhaps isn't as critical as an indirect, as the chamber tends to be more or less a steel tube. If you don't the air flow through the tube might be affected, and you could find carbon monoxide and dioxide levels raising, to a level where it is uncomfortable to work next to or in the worst case scenario dangerous.

Aspirated pumps - Special information.

Some cheaper heaters do not have the motor driven pumps like the Danfoss or Suntec which work on gears, but instead use an aspirated pump, or air pump which sucks air in at the back, and passes it over a tube going down into the tank thus creating the venturi effect and blasting fuel through the nozzle. These are particularly fickle, and any small amount of dirt on the air filters can affect performance. The images below show an aspirated pump in various states of assembly with filters:-

Diesel Heater - Aspirated Diesel Heater Air Filter Diesel Heater Air filter Removed

Diesel Heater Felt Filter Diesel Heater Felt Filter Removed

The above image show an aspirated pump. The first image shows the rear grill before removal. The two screws are for attaching a pressure gauge and altering the pressure. Try to avoid altering the pressure, usually sorting out all the other issues with a machine will mean the heater burns properly at the factory set pressure.

Behind that plate is a sponge air filter, as seen in the top row, middle picture. This can be cleaned in soapy water, but only replace when it's perfectly dry. It should be replaced with a new one every 500 hours, or when the pump isn't sucking properly.

Undoing the three or four allen bolts hidden behind the sponge filter (see top row picture 3) will reveal a second fibre filter. These don't tend to clean up very well. You should replace these as soon as they are clogged up. It can be worth washing the old one in soapy water while you wait for the part to come, but this will only be a temporary measure. These filters absorb a lot of water and can take a great deal of time to dry properly. Do not replace it until it's completely dry.

Behind the fibre filter are more allen bolts, undoing these will reveal the vane pump. This consists of a central graphite rotor with four inserts in slots. These can wear out, and will wear out quickly if dirt gets into the pump. You can try to clean them, but the assembly must be perfectly dry before it's replaced, or the vanes will stick and you will get no suction. These are a common part to wear out and you should budget to replace the assembly on occasion. If you remove the vanes and replace them, take care that if they are the type with a little 'v' cut out of one side - that side goes into the rotor and the straight edge runs along the outside. These pumps are very fickle and I suggest only opening the assembly to this stage if every other option has been looked at.

Another factor is the gasket between the air suction part and the air outlet. An old worn gasket will leak air and make the air pressure incorrect. If damaged replace, best practise - replace once every 12 months.