Gas boiler burner shuts off within a minute for no reason

Ted89

I have a newish Trio boiler with a Carlin gas EZ burner, indirect DHW tank, HydroStat 3250 plus base control, and a Tekmar 260 outdoor reset control. Working fine for 4 years. Lately, the burner seems to go on a lot with only domestic hot water demand and no space heat baseboard demand. Looking more closely, I see the burner comes on sometimes (not always) for just a minute, then shuts off, only to repeat many times until it stays on. Even when the burner turns off before demand or high limit is met, the Tekmar displays the burner icon indicating the switch is activated for the burner to light (but doesn't). The Tekmar #11 and 12 burner switch terminations correctly indicate continuity when the burner icon is shown.

Nothing to do with the Warm Weather Shutdown or Unoccupied mode. There must be a sensor somewhere doing this?!

What could to causing this? Thanks for any suggestions to check.

Ted

JUGHNE

My first guess would be flame sensor.
If you try space heating you may get the same burner cycling if it is a flame sensor.

Zman

You might try temporarily jumping the tekmar connections to eliminate the possibility of a flaky switch. If that is not the case, it sounds like the flame is not proving in the Carlin.

HVACNUT

Seems like its going into recycle, proving flame then dropping out and then it begins a new trial for ignition.
When was the last time it was serviced and had a combustion test?
Just curious, the 3250 Plus offers ODR. Why the Tekmar?

Ted89

Thanks for 2 great suggestions. I'll test tomorrow. How quickly would a flame sensor shut off the burner? Mine were as short as 5 seconds.
This is only a 4 year old system. Is the sensor something I could clean? The earliest appt with my serviceman is 6 weeks. Can't take a shower.
Thanks

JUGHNE

If you have a flame rod sensor, it should be cleaned every 1-2 years.
Scotchbrite pad would clean it up pretty good.
It is actually one part of a 2 component electrical circuit, the other is the grounded portion which could be the burner itself.
Both paths of conductivity have to be clean with good connections. The flame of the fire is between these 2 items and causes the electrical signal to be rectified from AC to DC.
If your flame control does not receive that constant signal it will shut down and retry.
Intermittent connections can cause your problem.

Ted89

Understand.
How quickly after a burner flame start would a dirty flame sensor rod shut it down?

Jamie Hall

Ted89 said:

Understand.
How quickly after a burner flame start would a dirty flame sensor rod shut it down?

Variable. Depends in part on just how dirty the rod is, and the characteristics (electronic) of the safety circuit.

Ted89

Could it shut it down in as little as 10 seconds?

HVACNUT

It's been 5 days. I know your service man can't get there for 6 weeks, which is utterly ridiculous, so it's time to find a new reputable HVAC contractor to repair the burner. And take out a maintenance agreement.

Jamie Hall

Ted89 said:

Could it shut it down in as little as 10 seconds?

I would think so. And as @HVACNUT says, six weeks is ridiculous. Find someone competent who can come sooner.

Ted89

Thanks HVACNUT
Just re-read your firstpost asking why a Tekmar 260. I had to think a minute on that. I had the Tekmar on the previous boiler before I converted to gas 4 years ago. If a 3250 Plus can do ODR and vary the target BWT accordingly- maybe i don't need it. But can it do DHW circulator priority over the space heat circulator with 3 ZVs? I know it can't do a port-purge. Thanks again

HVACNUT

@Ted89, no, the 3250 Plus does not offer post purge. It does offer thermal pre purge that will hold the burner off on a space heat call to dump stored BTU's to the emitters before firing.
And yes, it can be wired for use with zone valves. Diagram 3 in the manual shows the end switches from the zone valves connect to TT and the circulator for the zone valves to C1,C2 on the 3250. The indirect zone gets wired through ZR,ZC on the 3250.
Like most ODR apps, domestic priority overrides ODR and thermal pre purge.

Ted89

Thanks to all.
Paid for the 24 hr. guy to come out. It was a dirty flame sensor. And the entire chamber had heavy black soot. Trying to find possible causes. See my post, "VERY odd soot pattern . . .". For some reason I can no longer post a reply to that thread now.

Ted89

Thanks to all.
Paid for the 24 hr. guy to come out. It was a dirty flame sensor. And the entire chamber had heavy black soot. Trying to find possible causes. See my post, "VERY odd soot pattern . . .". For some reason I can no longer post a reply to that thread now.

Jamie Hall

Did your tech. measure and adjust all your combustion parameters? With instruments? It can't be done by eye. Heavy soot usually indicates that the combustion parameters are way out of whack.

Ted89

Thanks to all.
Paid for the 24 hr. guy to come out. It was a dirty flame sensor. And the entire chamber had heavy black soot. Trying to find possible causes. See my post, "VERY odd soot pattern . . .". For some reason I can n't post a reply to that thread now.

gennady

Why flame scanner got dirty? Why soot in the chamber? You fixing consequences, not the root of the problem.

Jamie Hall

@Ted89 -- as @gennady said, you are fixing consequences, not problems. There is something seriously wrong with that burner adjustment and setup, judging by your other thread...