Heater won't heat

[Serrano4657]

We have a motorhome with a heater. We have 4 register vents in the floor. When I turn the thermostat on I can hear the blower come on, but I never hear a clinking sound like the heater trying to light. Our last trip it took about 3 times turning the thermostat on and off to finally get it to light. All I get is air blowing, no heat. All the appliances work fine. I know nothing about heaters. I took the cover off the thermostat and it looks like it is working ok., but what do I know  ???

 

[scottydl]

On my motorhome, the fan runs for 1-2 minutes before the propane lights and warms the air.  Did you wait that long to wait for it to light?  The opposite is true too, if you manually turn off the furnace the fan keeps running for a minute or two after the flame goes out.

 

[John From Detroit]

There are several possible issues.. I see someone else covered one

When the fan comes on, assuming it is spinning fast enough, and there is nothing restricting the air flow, a switch, in the air flow, called a "Sail Switch" (Because it's operated by a sail) closes and then it calls for heat

Possible problems are Fan speed too low due to bad battery
Fan speed too low due to bad fan
Fan speed too low due to dirt on fan  (note "Fan" is most likely a blower)
Air speed too low due to obstruction in one of the air duts
Air  speed too low due to something covering one or more registers
Bad switch

Then we move to the control board

 

[Serrano4657]

I left it on for about 20 minutes and still cold air. No clicking sound. The heat used to come on after about 1  to 2 minutes. Should I try running my generator to get it to light? If the batteries were low, would the lights inside be low too, or not ?

 

[Ron]

I left it on for about 20 minutes and still cold air. No clicking sound. The heat used to come on after about 1  to 2 minutes. Should I try running my generator to get it to light? If the batteries were low, would the lights inside be low too, or not ?

Only way to determine for sure if the Batteries are ok is to measure the voltage at the heater.  Low batteries can cause what you are experiencing.

 

[scottydl]

You said "all the appliances work fine" but do the necessary ones work specifically on propane?  Fridge would have a propane mode, as well as hot water heater (I know that was brought up in another thread of yours), and stove burners.  There could be air in the propane lines, which can be purged by lighting the stove and leaving the burners on HIGH for 2-3 minutes.  Caution: stay close and make sure nothing flammable is near the burners during this process!!  Sounds obvious but we've recently been discussing MH fires and how to avoid them.

 

[Gary RV_Wizard]

We now have a an RV Furnace Trouble Shooting Guide in the forum library. Click HERE

The system is actually fairly simple and it is all explained in laymans terms in the guide.

 

[Old Soldier 1]

We have a motorhome with a heater. We have 4 register vents in the floor. When I turn the thermostat on I can hear the blower come on, but I never hear a clinking sound like the heater trying to light. Our last trip it took about 3 times turning the thermostat on and off to finally get it to light. All I get is air blowing, no heat. All the appliances work fine. I know nothing about heaters. I took the cover off the thermostat and it looks like it is working ok., but what do I know  ???

Not trying to be a smart alec, but did you check the propane tank to insure it was turned on?  Have propane in the tank?  If so, you can test to insure propane is indeed reaching the furnace by simply "cracking" the input line at the furnace and smelling.  CAUTION:  Do this in an open area, no source of ignition for the escaping gas in the area.  If you smell propane, immediately re-retighten the line.  Next, check for cob-webs or mud-dobbers in the air/gas mixing orifice.  Cob-webs have been notorious for causing furnace problems.  Once thats checked, if the furnace still won't light, it could be the sail switch.  If you know nothing about these items, you're advised to take it to an RV repair center.

Good Luck.

 

[Serrano4657]

Thanks Rv Roamer.

 

[Serrano4657]

I check the battery and it was reading 12.5 volts. Then I check the voltage at the heater and it was 10.5 volts. I turned on the thermostat  and within 30 seconds the heater kicked on and was blowing hot.  Do you think maybe because its not used very much it just takes time for it to light?  It took a while to get the burners to light on the gas cook top.  ??? ??? ???  Maybe there was air in the line?

 

[Karl]

Taking time for it to light is not uncommon if it's not been unused for a time - especially after you said it took time for your cooktop to work. Still, I'd be concerned about only 10.5VDC at the heater. Less than about 11 is marginal at best. Find out why it's so low.

 

[Gary RV_Wizard]

The low voltage may explain why it doesn't always light on the first try. Those furnaces are supposed to run down to about 10.5V, but below 11.3 is iffy for starting and the fan motor will run slow as well, making an internal overheat and/or poor combustion likely. Find and fix that voltage problem - likely corrosion on a terminal somewhere.  12.5V is not even good at the battery. While 12.6 is a theoretical full charge, the normal resting state for a recently fully charged battery  is more like 13.1-13.6. I'd say you have a weak battery and corroded connections.

And yes, your propane line probably has air in it - or maybe a failing regulator.

 

[Serrano4657]

I'll try recharging the batteries first, then go from there. I haven't charge them in a while but did add water not to long ago.