Truma Furnace: Basketball / Thumping Sound on Startup

[DunnYet]

Yep - me again. Reset 2.0 / Hull 1365 2023 LE II.

We are week into a two week loop, and I seem to be finding all the weird noises in the trailer. This one is the furnace. Rebecca describes it as "someone bouncing a basketball."

When the heater first comes on - regardless of just being turned on or cycling based on the temp, there is a metalic flapping sound that repeats for a minute to two minutes under the curb side bed. It sounds like something flapping up and down to me, Rebecca is sticking with her basketball metaphor.

It does not happen everytime, but I can't establish any type of pattern so far. Sometimes it happens as the furnace starts, just now it make two thumps as the furnace shut down.

Any thoughts or suggestions on what to check welcome. It's a maintenance / laundry day tomorrow, so good time to look at it.

[jd1923]

Be very careful my friend! Certainly, take a look inside.

 

Edited 12 hours ago by jd1923

[DunnYet]

7 hours ago, jd1923 said:

Be very careful my friend! Certainly, take a look inside.

Thanks @jd1923 - We were outside the recall numbers on the water heater - now I have something else to look for (LOL) 🙂

However, this is the air heater rather than the water heater. Same manufacturing (lack of) procedures could apply. I'm going to try to find any diagrams to of the overall system so I can possibly get an idea of whats in the airflow path that could stick / fail and cause the thumping noise.

[DunnYet]

Additional information - Temp this morning is 40 F degrees in Rawlins WY so I have time to track the cycles of the VarioHeat while enjoying morning coffee.

(1) Re-reading the VarioHeat manual from our Oliver year (2023) it appears that the "The appliance always starts at the lowest setting. If this is not sufficient to achieve the desired temperature in the vehicle, the appliance switches to a higher operating level after about 5 minutes."

(2) The "basketball" sound appears to occur more frequently at the state transitions between the low to high and the high to low, not on the off to low state transition.

(3) The sound seems to come from the outside wall area rather than from the point where the actual VarioHeat sits under the curb side twin bunk.

After the completion of the laundry sorting process this morning I will pull the bunk apart and see if I can isolate further.

[srthomsen]

8 hours ago, jd1923 said:

Be very careful my friend! Certainly, take a look inside.

 

I agree this video illustrates a problem with the water heater; however it doesn't address the issue with the furnace.

[jd1923]

3 hours ago, DunnYet said:

However, this is the air heater rather than the water heater.

Must have been getting tired last night! Truma in the title made me think HWH since there have been so many posts. Today I clearly see 'furnace' in title and body of post.

There is something called a "wall cowl" and several flaps in this system. One of them is banging when it changes speed producing this sound.