JB25PB for mobile homes:

The JB25PB is a tall, slim warm air heater designed specifically for installation in mobile homes. Although about 5ft tall it is about sevn inches wide so strikingly compact for the limited space available and comes with a 24Vac electronic room thermostat. Being for mobile homes it runs on LPG and I suspect the “PB” in the model number indicates “propane and Butane”. 

In principle it works in the same way as the larger J25-32 for houses, in that a simple gas burner with pilot light runs and heats a heat exchanger, over which a large quiet fan blows air which is thereby heated and ducted to warm air vents in each room. The electronic room thermostat turns the whole system on and off to regulate the temperature inside the mobile home and the room thermostat has a red LED to indicate when the boiler is running. 

There is no provision for hot water so I’d expect to find a separate appliance for hot water, usually an instantaneous gas water heater.

Common faults and fixes:

1) Pilot light 

If the pilot light goes out, the boiler won’t run and re-lighting it will be necessary. There is a round grey button on the Honeywell gas control valve which the user presses and holds in to send gas to the pilot light, which is lit by at the same time pressing the nearby black igniter button. If the spark sent by the igniter button fails to light the pilot flame (common!), a match or taper can be used instead. Once the pilot flame is alight, the grey button must be held in for about 30 seconds to allow the safety device, the thermocouple, to warm up. Then the button can be released and the pilot flame should stay alight.

2) Thermocouple failure

If the pilot flame lights but always goes out when the grey button is released, the thermocouple usually needs replacing. They are consumable parts and need replacing every few years.

3)

Gas valve failure

If a new thermocouple still does not result in the pilot flame staying alight, then the coil inside the Honeywell gas valve will have failed and a new gas valve will be necessary. This is a common failure with this particular gas valve which is fitted to many different models of boiler.  

4) Fan failure:

The motor in the air distribution fan typically fails every decade or two as the motor bearings become stiff with dust ingress. Oiling the bearings sometimes gets the fan running again for a few days or weeks but the problem returns and a new fan is usually required.

5) Room thermostat failure

On one occasion - after a power cut - I’ve encountered the electronic room thermostat failing. It is an unusual 24Vac thermostat so needs to be replaced with the correct equivalent which Johnson and Starley still supply as a spare part. The item they now supply is a Danfoss 24Vac room thermostat, model RMT-24. 

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JB25PB warm air heater photographed in a mobile home. This unit is tiny, only about 7” wide. The photo does not really illustrate just how compact it really is.