Furnace Ignitor Sparks but burner will not light.

[bdam]

I have an older Coleman Furnace, model 2985-766 which is refusing to light up unless coerced.  The gas valve is a Honeywell VR8450P6005.  I didn't mark down the igniter model, I'll do that when I get home, but I'm willing to bet it's one of the Honeywell S87 models. EDIT: I was wrong, it's a Fenwal 2940-325.

Here's what happens.

Combustion exhaust fan kicks in.

Pressure switch activates

Ignition sparks for a while and then stops.  Tries again in a bit.  Stops trying.

I can physically see the spark so I know that part is working.  No flame is seen at any point.

Here's the thing.  This happened around 10:00 last night and I was going through the normal troubleshooting routines.  At about 11 I hadn't gotten anywhere apart from noting the above sequence and was ready to call it a night ... a cold one mind you.  In a last bit of frustration I 'Fonzed' the gas control while the igniter was firing.  That is to say I gave it a love-tap using the side of my closed fist.  It lit up immediately and ran until the thermostat turned it off.  This morning it wasn't working again, I Fonzed it again, and it lit right up.  It ran for a few minutes, stopped, I Fonzed it again, and it ran until the thermostat turned it off.  Lastly, I hear the ignitor firing from time to time even after the burner has been running for minutes.

Any idea what the deal is?  My intuition is that the gas valve is not opening properly and by giving it a jolt it opens up, the gas flows, gets ignited, and the cycle continues.

[ACtechGUY]

Check for 24 volts at the gas valve between pv and pv/mv terminals when system is sparking. if you have steady voltage, problems in the gas valve (replace). If no voltage then problem is in the spark module or bad connection between module and valve. The sparking after ignition also indicates a faulty spark module.

Good Luck

[bdam]

Thanks for the response, it ran fine all day yesterday but I'll do that when it inevitably does it again.

Can anyone suggest the correct replacement part numbers for the gas valve and spark module just in case I have to go down those roads? Honeywell lists VR8305P2208 as a 'functional' replacement. I take it that when they say function they mean it's not going to bolt right in? For the module, Google comes up with some people selling IGMF527923 as a replacement but I couldn't find anything official on Fenwal's site.

[applianceman18007260692]

Check all your connections especially your burner ground. You have a loose burner ground I bet. Remove all wires and check for corrosion or rust.

[ACtechGUY]

Honeywell lists VR8305P2208 as a 'functional' replacement. I take it that when they say function they mean it's not going to bolt right in?

As Far as gas valves go a universal replacement of the same capacity and type should not be any problem as far as funcionality goes. Will the new valve be exactly the same physical size and shape as the old one?? probably not. Will the new valve Actually fit in the available space? This may or may not be a problem in the end. It just depends on design of the heater. Be careful of the height of the valve. If the new one is too tall , It may not be able to spin on without hitting something.

For the module, Google comes up with some people selling IGMF527923 as a replacement but I couldn't find anything official on Fenwal's site.

It looks to me like that module is the current replacement for that series of ignitors. you should have no problem using that part. It is very posible the only thing that is available anyway. That is a very old design spark module.

[bdam]

Thanks again for all your suggestions. As Murphy would have it, it didn't act up all weekend. So when I get a chance I'll clean up all the connections. If acts up again I'll check the power to the gas valve and go from there.

[bdam]

It looks like it was indeed the ground wire.

Apparently the genius who installed the main power grounded it by looping the ground wire around the screw that holds the panel on the small box that holds some of the electrical components. That screw rusted out making that connection spotty at best. I swapped the screws holding the panel on and it's been fine every since. I plan on moving the ground wire to the ... get this ... ground screw provided inside of that box.

[applianceman18007260692]

Glad ye could git er done.

[ManicMechanic79]

I assume you checked the voltage at the gas valve? If so I'd try blowing out pilot orifice. If thats not obstructed I think you will be looking for a new valve.