Overheating heater - Minimax millvolt CH 250M

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brdsng

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May 31, 2012
10
Hi,

I have been having issues with my heater this year. The fusible link blew out. If I jump the fusible wires to get the heater to fire back up, it runs for a couple hours and then seems to overheat.

When I initially turn the unit on, I am able to use the controls for on off and adjusting the temp. After a couple hours have passed, these controls stop working and the only way I can turn the unit off is to pull out my jumped wire or kill the gas.

Does anybody have any idea what this problem is?

Thanks for any help!
 
On this unit you need to remove the top to get to the heat exchanger to see if there are any obstructions. I would also suggest you remove the burner tray as well to see that there are no obstructions with them.

The overheating issue would not be caused by jumping out the fusible link/rollout switch. It is used in case flames should roll out from the burners. Now that can happen if there is an obstruction with regards to the burners or the heat exchanger.
 
After I found the fusible link blown, I washed the entire thing down with the hose. Spraying everything possible internally, seemed like I got quite a bunch of stuff out I've used the heater for probably 8 hours total, wouldn't it have burned anything out by now?

either way, I'll get the cover off and check it out if this is not pointing to the electronic stuff.

Thanks!
 
Yea, I killed the gas to it and when I was spraying it down, I made sure not to get the controls wet. Blew it out with my leaf blower and then let it dry and then fired it back up.

Do you think after all that and running it for about 8 hours there could be something still not exhausting properly?

Did I do damage to it with what I did washing and blowing it?

Thanks again
 
ps0303 said:
Well if it's working now and no interruptions, then you may have taken care of the issue.

So is it in fact heating as it should?
Click to expand...

No, that's what I was trying to say, it's still overheating. Do you think after all I have done, there could still be an exhaust issue? I haven't replaced the fusible link, I just have it jumped still. I can run the heater for a couple hours but at some point, it will overheat and I guess and the controls stop working. I can't control temp to turn it off or use the switch, I just have to unjump it or kill the gas. I'd assume that if the fusible link was in there at that time, it would blow again.

I'll be home in a bit and will take it apart if you think there's still a possible obstruction.

Thanks
 
Well You can't run it with the gas valve jumped out.

So lets start from square one. The heater won't light on it's own, correct?

Is water flow to the heater good? NO bypasss valves or anything impeding the flow of water to the unit?
 
The fusible link is currently blown due to I assume overheating last summer, I was never informed of this.

This year,I couldn't get the burners to fire but the pilot would light. I finally figured out the fusible link is blown.

If I jump the fusible link, everything starts to work as it should, immediately fires up. At that point,I can turn on or off with the switch and control temp with dial.

After about two hours, the controls stop working,I cannot use the switch or dial to turn it off. So I have to pull the jumped wires apart to stop the burners.

After it cools, I can repeat everything until it again overheats about two hours later.

I've tested all the safety sensors and they all seem to be fine.

Does this still point to exhaust blockage, taking into account everything I've done with flushing everything out with the hose and approximately 8 hours of run time.

Thanks
 

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OK. The fusible link is there for any type of rollout condition where the flames from the burners would rollout under them and back towards the front of the heater. Commonly a blockage or even a down draft could cause the flames to rollout like this.

Jumping out the fusible link should not cause the thermostat control on the heater to stop working. If you jumped out the gas valve, you would be bypassing all safeties and thus you could cause an overheating issue but you are not doing that. How hot is the water getting?

Can you see the flames and if so, are they really tall and not blue?
 
The gas valve is not jumped out, the only thing I have jumped is where the fusible link is supposed to be.

The flames seem to start blue and low and then when I check it after a couple hours, after I've lost control of the unit, the flames seem larger and orange.

The water coming from the jets seem normal hot.
 
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