Long run issue with the Nest

nybz

I know the nest isn't anyones favored smart Tstat for steam. I was given one for free by my brother whose contractor said was the wrong model for his system.

So far it has been working okay, was hoping to test set backs, but am still just leaving it on 1 temp since it's been mild and barely runs anyway, not much for it to learn yet.

Today though my wife and I woke up to a Tstat set point of 69 but the Tstat and all the remote sensors were well into the high 70's even high 80's in our bedroom. Even with lowering the set point and telling the app to shut off the boiler was still running, and not building pressure since my big mouths were apparently open and spewing steam again, an issue I thought I semi-resolved. I cut the power to the boiler as it was 3:00am and I didn't have the ability to think about what was wrong. Before I left for work I turned the power back on and the boiler immediately kicked on again so it's still off as of now.

Does anyone know of what could be the cause? I figure when I get home I'll turn it back on and see if still runs, and for how long. It could just be nest charging itself, but that wouldn't explain the initial extended hot run?

I'm thinking it could be a short in the old wiring to the Tstat?

Thanks!

STEVEusaPA

Define "...all the remote sensors..."
Could be a short which you can test with a multimeter. Or run a new temp wire and see if the same problem persists. Ideally if the boiler won't stop running and you disconnect the thermostat wires at the control, and the boiler still runs, it's not the wires or the thermostat, but probably one of your controls, like a safety control that should've shut down the boiler.
Best not to run it without getting it professional serviced. Run away steam boiler is a potential bomb.

nybz

I have the nest and 3 remote sensors for it around the house.

I'm not sure a pressure control would have triggered anything since both big mouths were open and spewing steam.

I figured I'd check it again, with my old Gortons back on. Maybe also with my old honeywell Tstat, and if it still seems like an issue I'll find someone to call and inspect

HVACNUT

A lot of faulty sub bases on the Nest. Shorted contacts. Try removing the W wire at the thermostat.
Is the Nest 24v powered or its using R and W only?

nybz

At the moment only by the R and W

I bought a new Tstat wire I might install with a plug in transformer at somepoint down the line, but it was working without for now. I'm guessing the wire it is using is the original wire, the house is from about 1920.

nybz

The thermostat wire was spliced near the boiler, I undid the splice so no connection is being made anywhere in the walls to the thermostat. It shouldn't run, yet the boiler still runs on its own when I turn on the cut off switch?

I'm making a call to someone who has serviced it but figured I'd see here also

mattmia2

The wire was likely installed whenever they replaced/converted the coal boiler to oil or gas.

If you disconnect the TT wires at the boiler control and it is still running then the issue is with the boiler controls.

I assume that 3 wire t-stat wire ran a 2 stage boiler that is long gone.

HVACNUT

If the burner still runs with the TT wires off, shut the system down at the circuit breaker. That is an unsafe condition and needs to be serviced by a competent oil heat contractor. Like now.
Post back about the repair and share the combustion report results.

nybz

So I disconnected the two contacts and when I turned on the power it turned on, but i tested after reconnecting them and now it's working normally again?

mattmia2

Probably something like a contractor on its way out that welded together or otherwise stuck, still should not be operated until it is sorted out.

Jamie Hall

Sounds very much like a sticking relay in the burner control. As the folks above said -- turn it off at the breaker and leave it off until it can be serviced.

To amplify -- if a burner control relay is sticking on, none of the safety controls can shut the thing off. This you do not want...

nybz

No combustion report of anything just now, but I had someone quickly come out and swap out that burner control. Hopefully that prevents that from happening again.
I probably will try to get it more professionally serviced/repaired/cleaned down the line.
Thanks all!
And sorry Nest, for blaming your product

mikeg2015

> @Jamie Hall said:
> Sounds very much like a sticking relay in the burner control. As the folks above said -- turn it off at the breaker and leave it off until it can be serviced.
>
> To amplify -- if a burner control relay is sticking on, none of the safety controls can shut the thing off. This you do not want...

That’s why I like LWCO to open Incoming 120vac.