Hot Dawg issues

billtheplmbr3845

Hello, I went on a no heat call for a customer. Hot Dawg HD-75 in a garage installed 15- 18 years ago. The heater goes thru the proper ignition sequence, hot surface igniter lights up, gas valve opens, gas comes into tubes, but nothing lights. I have 6.5 in. wc at inlet tap and 3.5 at outlet tap, right in the listed specs. I can get the burner to light if I hold a lighter at the end of the burner tube that has the igniter, it will run fine but then won't re-light. I took the manifold apart and checked the orifices for obstructions, nothing there. Everything seems to test fine but I HAVE TO BE MISSING SOMETHING. Any one have any suggestions. I'm stumped. Thanks in advance, Bill

neilc

someone else here with more knowledge than me will tell you to ohm the igniter for spec,
but if your seeing it glow bright then I would make sure the burner tubes are clean also, maybe some of them little holes facing the ignitor are ugly,
when it lights off do you see steady flame there ?

billtheplmbr3845

Original ignitor wasn't glowing all the way so I replaced it. Now it is bright orange all the way across. When it lights with the lighter it runs great, the slot in the burner tube linking them all together has flame, and all the tubes light instantly with no delay.

neilc

yeah,
but if the jet or 2 that blow to the ignitor are dirty,
maybe from the weak ignitor prior to its failing, maybe backfiring a bit , , ,

IDK the configuration in that unit but my home furnace lights from the extreme right burner, crosses the 3 tubes, before making my flame rod to the extreme left

you know your flame sensor is good cause it stays on,
why isn't the gas igniting on the new ignitor?

billtheplmbr3845

I don't know why its not igniting, I evan disconnected the HSI and put it right in front of the burner tube and jet, still nothing. I know the jets are clear because when it lights, they light also.

neilc

maybe the valve is slow(ed), and there's a slight delay in gas flow?
can you hear it / feel it snap open ?

garages are dirty dusty,
I would still pull that burner tube and double check

billtheplmbr3845

Opens and gas comes out, I was considering turing up the manifold pressure to 4 or 4.5 and see if that helps

neilc

I'm tapping out, good luck,
maybe someone else can jump in.
keep it in spec
@Tim McElwain

billtheplmbr3845

Im sure its going to be something simple im overlooking. I evan called my freind Chad, the local heating genius and he came up empty.

ratio

Can you hold a match RIGHT where the HSI is? The only thing I can think of is that the gas isn't making it to the HSI in the right concentration for ignition, or that the HSI isn't igniting it. A flame at EXACTLY the right spot should tell you one or the other. Maybe even move the HSI out of the way first.

billtheplmbr3845

Did that and it lite. The HSI i put in is solid, the original is supposed to be a cut out style (found a broken piece in the burner tray), I was thinking maybee the gas could pass thru easier. The solid one had been working since last year.

HVACNUT

Are you using a universal HSI?
Exact location of the OEM?

billtheplmbr3845

Universal Hsi, seems like same location. The heater had been working with the universal hsi untill about s week or two ago

neilc

ah, ya might need that OEM cut out

billtheplmbr3845

I was thinking the same but its like 70.00, and it may not solve the problem. It worked with the universal ignitor before

Leonard

dumb question...... but has building been vacant or a line shut off for ~ > 6 months, need to purge air out of gas lines??

Wondering if Gas/air ratio is too low to light with glowing type igniters. No experience with these ignitors..

Fred

Check for a spider web in one of those tubes. Amazing how a spider web can block gas flow. Ask me how I know.

Tim McElwain

The fact that you can light the burner with a match says the gas valve is good. It sounds like you have a problem with the gas/air adjustment. Soften the flame up by reducing the primary air.

billtheplmbr3845

There are no air adjustments on the burners. Do you think the oem ignitor would be better than the universal?

ratio

Seems like something to try. Tech support won't be too interested in helping until all factory parts are installed.

Tim McElwain

The only problem with igniters is that some have higher resistance than others and may not match up with the electronics on the system. There are igniters which are 34 second igniters and other are 17 second igniters. What is the trial for ignition time for your system. That igniter has to get up to at least 1800 degrees in order to ignite the gas. I would go with the original igniter and see what happens. By the way there are other ways to control air on burners even if they do not have air shutters. It has to do with the positioning of the burners relative to the type of fuel.

Tim McElwain

Were the Universal igniters from Robertshaw? If so those igniters have to have a seperate flame sensor as they do not sense flame.

billtheplmbr3845

I will try the oem ignitor and see what happens. The orfices are in a pipe, this mounts in holding brakets at the end of the burner tubes and the braket with the orfices screws to the heater body, there is no movement in or out with the orfices

billtheplmbr3845

Not Robert Shaw, there is a separate flame sensor on the bottom burner tube

HVACNUT

> @billtheplmbr3845 said:
> Not Robert Shaw, there is a separate flame sensor on the bottom burner tube

So this is a horizontal furnace, atmospheric with induced draft?
And with 3.5" manifold pressure it's natural gas and not LP right?
The whole circuit is proving right up to the point of no ignition, with (what seems to be) a working HSI.
It quacks like a duck. Put in an OEM HSI, or at least cross reference that furnace for a universal.
Also, I'm sure specs say 3.5" manifold so do not adjust.

clammy

not to sound stupid but have you chked that u have constant inlet pressure while trying to light had a issue recently with a bad gas regulator worked for hot water heater but could not reliable get the hot air furnace to run and the mod con locked right out .Quick chked w a manometer and i had it fiqured out gas pressure reg sticking HO who is a tech had replaced the furnace hsi and gas valve and flame sensor just kept thinking it was the furnace but it was the gas pressure .Funny was the hot water heater was just fine and teh pilot never went out and she always fired odd stuff .peace and good luck clammy

clammy

Have u chked the inducer fan centrifagal switch or pressure switch to make sure it s made if so equipted peace and good luck clammy

newagedawn

i agree with the pressure switch wont stay closed or have you checked the flame sense, not the ignitor, thats the only thing i can think of as to why the gas valve wont stay lit and quite frankly its the only reason

billtheplmbr3845

Gas valve stays open fine when lit with a lighter, just won't ignight on start upwith the HSI

billtheplmbr3845

Just saw this old post, I installed the oem HSI and the unit lite snd worked fine, lesson to this stiry is don't skimp out and use original parts if possible

HVACNUT

> @billtheplmbr3845 said:
> Just saw this old post, I installed the oem HSI and the unit lite snd worked fine, lesson to this stiry is don't skimp out and use original parts if possible

Nice!