Heatmaster C-375 / MF 7000 trouble - fire goes out

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

Jsheds

New Member
Oct 18, 2021
3
Eastern PA
Hi All, new to the forum. Thanks for having me.

I'm a new owner of a Heatmaster C-375, burning wood. I'm new to this furnace, but not OWB, it replaced a CB 6048 that I had for 14 years. This C-375 looks like a good unit, well built and very happy with it, except I can't keep the fire going. It's heating my shop and it is cooling off here in eastern PA so I should have enough of a heat load to keep this thing going, but I can't.

I have called my dealer and discussed with him, I have called Heatmaster and discussed with them. I'm told I've done everything correctly, but obviously not, hopefully I can get some help here. So here's the story; It should be as simple as build a fire, keep wood in it. I started with a differential of 10 degrees and high limit of 180. I'm burning red oak that has been split and dry for 2 years along with some dead ash, but mostly oak. My splits are 4 to 6 inch size with some 8 to 10 inch all about 18" long. Once the water is up to temperature, the furnace shuts down and does not restart. I left the house this morning with and the furnace was hot. I went home at lunch to check on it, temp was at 155, blower running and no fire, lots of wood and charcoal.

I have tried every combination I can think of for differentials from 2 degrees to 10 degrees and high limit from 180 down to 165. I have loaded wood all the same direction, different directions, in the front of the box, back of the box, on the side. Mixed wood large and small, all large, all small, keep the ash pan clean, etc. I can't figure it out - it shouldn't be this hard. There isn't an air flow problem when the blower is running, plenty of air, maybe too much. I don't think I'm hitting the high limit that shuts down the furnace since the fan is always on, and I've never seen the temp over 183.

The only helpful information I got was from the corporate office. There is a small hole below the fan with a flap on it to allow air into the firebox between burns. This isn't shown in the manual, and it was closed. Once I opened that, it burned for 2 days with no issue and then back to normal, no restarts. He also suggested a lever on the bottom that limits air flow into the box, but my unit doesn't have that.

When I open the door and it's out, there is plenty of wood, but no coals, lots of charcoal, but large pieces.

I'm not here to bash the dealer or manufacturer, just trying to figure this out. The manufacturer has a good reputation based on the reviews I've read. I also realize they market this as a coal furnace. According to the dealer and person I talked to at corporate it is identical to the MF series that is rated for wood. It shouldn't be this hard.

Thanks for any help you can give. I'm open to any suggestions, I really want this to work.
Jim
 

E Yoder

Minister of Fire
Jan 27, 2017
598
Floyd, VA
It's a new furnace with not much ash to insulate the coals. So the coals lay on the grates and go out.
A deeper ash bed will do wonders for it. Also leaving the little air leak hole wide open helps. If you start getting lots of creosote in the chimney you're letting too much air in.
I hear this frequently with new furnaces with no ash bed, but the C models most often. It will get better with colder weather and more ash.
 
  • Like
Reactions: brenndatomu

Jsheds

New Member
Oct 18, 2021
3
Eastern PA
It's a new furnace with not much ash to insulate the coals. So the coals lay on the grates and go out.
A deeper ash bed will do wonders for it. Also leaving the little air leak hole wide open helps. If you start getting lots of creosote in the chimney you're letting too much air in.
I hear this frequently with new furnaces with no ash bed, but the C models most often. It will get better with colder weather and more ash.
Thanks for the reply. I've been running for about 2 weeks and can't build up a bed of coals, everything falls through. Any suggestions? I've tried loading more wood but no help. Everything burns to a fine dust.

Have you seen any with the new damper motor? This is the first one my dealer has seen. It's not in the manual that came with my unit, that still shows the old solenoid. I did find a 2021 manual on the web site, but the adjustment instructions don't match the current setup. Curious if that may be an issue or just an oversight.
Thanks,
Jim
 

brenndatomu

Minister of Fire
Aug 21, 2013
6,600
NE Ohio
Do you still have your old CB? Or know someone that has an existing wood burner that you could get a bucket full, or two, of ashes to dump into yours? Might sound dumb, but I find almost all modern wood burners do better with a bed of ashes in them, and I actually save a bucket full when I do my spring cleanout to scoop back in at first fire in the fall (coming soon here)
 

E Yoder

Minister of Fire
Jan 27, 2017
598
Floyd, VA
I'd dump the coals and ashes in the pan back on the grate. Keep recycling.
A plate over the grate works sorta, but you won't need it as soon as you pack some ash in the firebox.
They switched from the solenoid to the damper actuator this year, the actuators on the G models have been so reliable the thinking is why not do the same on the C's. But the solenoid was the old faithful for years, I think either is fine.
There is a way to make the actuator open a percentage so that's why the manual damper was eliminated. I don't remember how to do it though, but throttling back the burn isn't the answer in my opinion.
 

brenndatomu

Minister of Fire
Aug 21, 2013
6,600
NE Ohio
Don't some people with coal units end up putting a plate over their grates? Or am I out to lunch?
That was the key to getting my old Yukon wood/coal burners dialed in a lil "better"
 

Jsheds

New Member
Oct 18, 2021
3
Eastern PA
Thanks for the replies. I had considered adding a plate to restrict air flow, but that just seems wrong. I actually got it to burn through the night last night, I'll add some ash back into the fire box and see what happens.
Thanks,
Jim