Jumpered Safeties

Alan (California Radiant) Forbes

High limits, flame rollout switches, spill switches…………never, although I've seen a few; usually on flame rollouts because tech's. are too lazy or too scared to further investigate clogged heat exchangers or insufficient flue draft.

But my resolve never to jump a safety was tested today on a Viessmann Atola with a bad sequencer which is not really a safety. In this case, it allows the inducer fan to power on before ignition. The owners had no DHW, so I jumpered the sequencer to heat the indirect. I wanted to leave the jumper in place until the new part arrives, but I knew I would never get to sleep tonight.

What could go wrong?

mattmia2

it could blow up a little if the combustion chamber contains the right amount of gas. couldn't you just have got a sequencer?

EdTheHeaterMan

I find that jumping a safety is a temporary fix or test to eliminate or confirm that a particular part is in fact the cause of the problem. Once you have determined the issue DO NOT leave a jumper on a safety control unattended. Only jump the device when you are there to remove the jumper in the event of a problem. Once you leave the jumper MUST LEAVE with you.

EBEBRATT-Ed

Alan,

if I understand you correctly only the inducer would not start so you jumped 4 & 5 on the sequencer?

If you did that the inducer will probably run 24/7. All the safety's for the burner are still in the circuit. No harm done at all.

Part of the wiring diagram is chopped off but if the burner cycles on thermostat and the inducer runs all the time so what you can leave it that way until you get the part.

I don't see any issue with doing that

pecmsg

Was taught in the UA classes if you're going to jump a Safety you get to stay and be the safety!

Jamie Hall

Technically, if you jumpered four to five on the sequencer, that's not a safety in the usual sense. Rest easy,

Alan (California Radiant) Forbes

I jumpered 1 and 3 and figured the fan would be on long enough to satisfy the pressure switch to remove any gas. The pressure switch is between 3 and the ignition control module, so there would be a short pre-purge.
I’ve had very little experience with sequencers and didn’t know you could buy one off the shelf. It’s arriving tomorrow from Viessmann.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1801176#Comment_1801176

there are thoughts of an emergency mode for my ac to run off of generator involving a sequencer that starts the condenser then starts the furnace blower 10 seconds or so later after the compressor has had a chance to start but before it noticed a lack of load on the evaporator. I suppose I could do the same with the condenser fan and a 240 v sequencer.

Teemok

I think that sequencer is there to provide A: delay the ignition module initiation for inducer pre-purge time. And B: inducer on hold after the call drops for post purge. Jumping 1 and 3 leaves the pressure switch as the ignition operator and shortens/eliminates the pre-purge delay. That's the risk. If there's a small gas leak or any source of combustibles around that build up and the ignition module is started before it's cleared out by the correct per-purge time, then it combusts in an undesired way. In a critical must run pinch, bad 1 - 3 contacts could be replaced with a delay on make device but factory parts are always the way to go. I agree with all that's said above, leave no jumpers in place.