Oil Burner Expected Behaviour ?

DrBass

Nest thermostat calling for heat at 20* Requested Temp 21* - Burner fires - Rads heating up as normal - Burner shuts off before Nest thermostat reaches 21*

I notice this, so go to the outdoor oil boiler and turn up the the boiler thermostat from 70* to 85* it ‘clicks’ all of a sudden the burner fires up again. 

Whats the reasoning behind this? and would this be expected behaviour? 

Wearb

First the nest seems to predicting heat requirements. So that's normal. That feature can be turned off if you want AFAIK.

On the boiler, that controls the temperature of the water heating the rads and is normal. I'd leave it at 70 or 75 unless there isn't enough output out of some rads to heat a particular room properly.

John.G

A oil fired boiler has a fixed output and cycles on and off depending on the heat load, it only looks at its own boiler stat so if set to 70c then will fire up when the boiler temperature falls to ~ 60c and cut out at 70C. The nest is looking at a room temperature and if the temperature is < the requested temperature it still requests full radiator(s) heat but the boiler may be rated at say 26kw and the rad demand may only be 15kw so the boiler will cycle on and off, oil fired boilers spend their whole lives cycling on/off, you will generally only hear them firing continuously for ~ 25/35 minutes in the morning after a cold start as they also have to get the system water contents of ~ 75/100 litres up to temperature.

DrBass

@John.G

Thanks - this was exactly the explanation I was looking for. It makes total sense now, lots of really good detail in this answer for me to understand better.

listermint

Don't forget to put the safety thermostat back to where it was.

John.G

You probably mean the control stat?, to reduce it from 85C to 70C ish

The safety (hi limit) stat is non settable and fixed at ~ 113C, if it operates, then has to be reset manually.

DrBass

Ok didn’t know it was tripping at 113*. I’ve moved the control stat back to 70ish.

Boiler went into lockout mode again today, had a run of 3 days without a lockout. Intermittent lockouts for the last months have me a nervous wreak.

jimf

when you say lockout what exactly do you mean

and how do you get the boiler to fire back up again

are you resetting the stat on the boiler or the reset button on the burner

DrBass

Red Button Burner LockOut - Press Red button in 5sec - Burner fires up. Works away then for a few days at best.

jimf

red button on burner means you have a burner issue rather than a system error

intermittent issues can be a balls to identify but there are a few things than any boilerman will look at first

it could be as simple as a capacitor or a photocell or a tight spot on the fuel pump dirty filter at the tank as you can see there are quite a few