HeatNGlo pilot ignition not working correctly

[GaryREM]

We have a 29 yr old fireplace with pilot ignition. When we turn it on the main flame does not ignite after several seconds. However, when switch is turned off, the main flame near the pilot will ignite, so flipping it back on results in the main flame properly igniting. This works somewhat consistently (although some times we have to turn on and off a couple time).

Any obvious thing to look for?

 

[DAKSY]

What fuel are you burning?
LP or NG?

 

[GaryREM]

What fuel are you burning?
LP or NG?

It’s natural gas.
And it’s a 19 yr old unit...

 

[DAKSY]

It may be time for a new pilot assembly.
When was the last service done on this unit?
Which Model do you have?

 

[GaryREM]

It may be time for a new pilot assembly.
When was the last service done on this unit?
Which Model do you have?

It's an SL-750-TR.
Service? It's never been serviced

 

[DAKSY]

OK. Do you have a millivolt tester?
Do you have other basic hand tools - wrenches, screwdrivers & nut drivers?

 

[GaryREM]

OK. Do you have a millivolt tester?
Do you have other basic hand tools - wrenches, screwdrivers & nut drivers?

Sure.

I thought the issue seems to be that the pilot is lit but doesn't light the burner until I turn off the valve and the pressure goes down. Once lit, the burner works fine. But, I am NOT experienced with this stuff, so open to expert suggestions.

 

[DAKSY]

Ok. Let's start with the thermopile (TP). It is the larger of the two sensors in the pilot flame.
Leave the burner off & take a reading on the TP
There are terminals on your valve labelled TH, TP & TH-TP (or TP-TH).
Set your tester to vDC & touch the probe tips to the screws labelled with TP ,
& hold them there for a little bit. Maybe 30 seconds...
What reading do you get?
Is it holding steady or fluctuating?

 

[GaryREM]

Ok. Let's start with the thermopile (TP). It is the larger of the two sensors in the pilot flame.
Leave the burner off & take a reading on the TP
There are terminals on your valve labelled TH, TP & TH-TP (or TP-TH).
Set your tester to vDC & touch the probe tips to the screws labelled with TP ,
& hold them there for a little bit. Maybe 30 seconds...
What reading do you get?
Is it holding steady or fluctuating?

The TP is putting out 333mv with no variation with just the pilot on. (That seems marginal).

 

[DAKSY]

WAY low. You should be around 525 +/- 25 on that.
They are about $60 at True Value...
They offer a universal millivolt generator.
The burner side magnets will draw about 200 mV & that
takes you to about the minimum mVs (~115?) to keep them open...

 

[GaryREM]

Yup. And this makes sense that the valve isn't opening as it should. Will replace and see what happens. Thanks.

 

[GaryREM]

New thermopile should arrive today.

Looked back in my files and I realized that I had replaced the pilot assembly back in 2010 (10 yrs old). Its 10 later and we'll see if swapping in new TP does the trick.

 

[GaryREM]

Decided to replace entire pilot assembly (thermopile, thermocouple, pilot, igniter) since I was taking things apart and it was only a little bit more work.

The good news is that the burner ignites quickly.

The bad news is that the millivolt reading only increased to around 424 mv. That is surprising. Expected more significant change. Pilot flame looks good so not sure what’s going on.

 

[DAKSY]

Have you checked the gas pressure?

 

[GaryREM]

No, I have not.

The pilot looks fine (I think ) and the burner flames look very strong.



I've got 2 furnaces (just had winter maintenance check on them), water heater and range on gas that all seem to be working fine, so haven't considered pressure a possible issue.

Assume you are talking about checking at the fireplace, but don't have a manometer.

 

[DAKSY]

That's a LOT of appliances on a gas line...
Without getting into specifics, NG works
on volume, so pipe diameter is important.
Yes, there are gas ports on the front of the valve,
which allow you to check the incoming & outgoing (manifold)
pressures with a manometer...

 

[GaryREM]

Finally checked pressures.

Inlet pressure: 6.6 in w.c. (fireplace indicates 5 in w.c. min)
Manifold pressure: 3.9 in w.c. (fireplace indicates 3.5 in w.c. min)

 

[DAKSY]

Those numbers look good.
are you able to adjust the pilot?
IIRC, there is a Chrome slotted screw on the front
your valve that needs to be removed.
There is a pilot adjustment screw behind it.

 

[GaryREM]

There seems to be little adjustability on the pilot.

Removed the screw covering the pilot adjustment and saw no change in the pilot by moving the screw in or out.

 

[DAKSY]

When you replaced the pilot assembly, was a new pilot tube included?

 

[GaryREM]

Yes. I figured that it was almost the same effort replacing thermocouple, thermopile, pilot and igniter (although clearly more expensive ).