Noble Combi boiler + Nest thermostat combination sometimes works, sometimes doesn't!

bostonab

I've run into a weird problem, wondering if anyone else has? I had this boiler installed late last winter, and because of work-from-home this winter, am actually seeing it work, and see it behave oddly.

Sometimes, I set the thermostat on one of the zones at 5 or 7 degrees above what it's reading, the circulator light immediately turns on and the exit from the circulator very soon turns hot to the touch, as it should, and the baseboard heating gradually starts warming. However, this doesn't *always* continue till the room heats up to the desired temperature: *occasionally* I find that the circulator light stays on, but the exit pipe is *not* hot, even when the room temperature is still significantly below the setpoint. In these instances, the room takes a long time to heat up. When this happens, I've tried resetting the setpoint in the thermostat, and sometimes everything starts working again. There's no reproducibility to this behavior, and it affects at least 2 or 3 of the zones in my 4-zone system - I can't categorically say that all the zones have this problem or not.

Is there some setting on the boiler that has to be adjusted, that I need to be aware of? Or is it something to do with the interaction between the Nest thermostat and the boiler? Would appreciate any insights/feedback, thanks.

Jamie Hall

Are there zone valves for your various zones, or does each zone have its own pump?

And by circulator light, do you mean a pilot light on the circulator pump itself, or something lighting up on the thermostat?

There are many many different ways to pipe and wire these things, so a bit more information would be helpful.

bostonab

Hi Jamie,

Each zone has it's own Taco 007e circulator pump, 4 in all for the 4 zones. Each pump has an orange indicator that lights up when running. These are the lights I was referring to, in my description.

Thanks,

AB

ratio

Do all of the zones exhibit this behavior, or just one?

If the pipe isn't getting hot, the hot water isn't moving. If a light on the pump is coming on, that tells me that it's getting the signal to run, so it isn't likely to be the Nest (this time!).

Does the pump feel like it's turning inside? Put your hand on it & compare it with another that you know is working. Is it too hot to touch?

bostonab

I thought it was happening on 1 zone, but it happened on another recently, so I'm not sure whether all zones behave this way or not. This isn't happening all the time, so it's hard to isolate.

I'll check on your suggestion re: the pump being hot, have to wait until the problem happens again.

Ironman

Your problem: the Nest. Get rid of it. It's for the birds.

tim smith

Most important thing on Nest is that you have a C wire to nest sub base. Erratic behavior with Nests are common without a common wire. Check base and see how many wires are connected and to what terminals. Maybe post a pic of sub base and interior wiring of Taco zone control.

ratio

If the pump's light is turning on every time, it's getting the giddyup command & therefore it can't be a Nest problem, although, there is the possibility of a misunderstanding.

My guess, frig what I've read, is a failing pump (loose rotor, overheating, etc.), but there are others here who's guess will be better than mine.

neilc

haven't I seen circs where the light changes color ?
green for go, red, maybe blinking, for - hey there's a problem ?
and in my case, the motor was mounted vertical up, and was air bound, and I will never stop bugging that plumber about that , , ,
OP,
can we see a picture of your circ(s) ?

BruceA

as tim smith wrote, check C wire

bostonab

Hi All, here's an update:

I had the plumber who installed the system come by to check things out. Of course when he came by, the problem wasn't showing up

However, he did confirm that it probably wasn't because of the nest for the following reason: whenever the actual reading in the room is below the temperature setting, the light on the circulator does turn on indicating that the thermostat is asking for heat and the system is indicating that it has received that signal.

Now as to why the signal is not being acted on occasionally: he found that the flow indicator for the hot water demand was not set correctly: at times, even when there was no hot water usage in the house, it was indicating that there was usage. Apparently, when this combination boiler senses hot water usage it prioritizes that over the heating function, resulting in the heating being interrupted for that duration. Since this was a sensor/setting fault, which presumably could randomly trigger the override, I was seeing that effect on my heating system.

The above explanation seems plausible; the plumber made some changes today and I'm waiting to see if that fixes things.

What do you think, does that sound right to you?

ratio

Makes sense, fits the symptoms; I might be biased because he agrees w/ me re the Nest being innocent of the fault in this particular instance.