Boiler acting strange since Nest installation

[Mekrel]

I had a 'Nest Pro' install the Nest V3 we brought with us from my previous property.

I hooked it up previously as it was a simple wire up to the combi boiler, but the new house is on a unvented system. From what I can gather, the installer removed the old programmer (and I assume bridged some connections together), then installed the Nest Link near to the hot water tank so it controls the 2 X motorised two way valves (one for HW, the other for CH).

Literally since the install happend, the boiler will occasionally not fire up when needed. The Nest installer said the Nest is doing what it should, which I agree as when hot water or central heating is requested by the Nest, the valves are opening, the pump is running and there's a orange light on the boiler that shows it knows it should be providing hot water.

It's an oil fired boiler, and if I press the reset pin in, it fires straight up. We had a guy come around to check over the whole system, he said the reset pin I'm pressing usually only needs doing if the boiler has shut down due to overheating. He reduced the thermostat on the boiler itself, but it has still been hit and miss firing up.

Is there anything I'm missing? It seems too much of a coincidence this has stated since the Nest was installed but at the same time, the things the Nest controls seem to be acting as you would expect?

 

[cuke2u]

As with my Tado and an oil fired system, if water is hot enough in the boiler flow pipes then it'll be in a ready state, orange light on and pump running.
There also should be a over heat light on the boiler if it's overheating.
What make and model is the boiler and did the guy check the thermostat and if the motorised valves are opening? Is it a y or an s plan system?

S and Y Plans Explained

Most homes are fitted with either a Y Plan or S Plan heating system. Here, we explain the difference between both systems.

www.warmzilla.co.uk

 

[Mekrel]

It's an S plan system.

The boiler is a Grant Vortex Eco, we both checked the valves - you can hear them opening and closing, and the control arms have free movement.

I'm confused by the boiler manual if I'm honest, in two areas.

1) There's a small light on the switch, the manual says "Wall hung boilers have a ‘mains on’ neon, see Figure 2-2, which lights when the boiler is switched on." and then right underneath that "The ‘mains on’ neon light does not necessarily indicate the burner is firing."

The strange thing is, that light doesn't show when the boiler is turned on and no hot water is being requested.

2) the manual also states the thermostat on the boiler should be equal or greater than the thermostat temperature set on the hot cylinder, but there's no display or marks on the knob that tells you what the boiler thermostat position translates to in temperature.

No overheat light, the only lights are the 'mains on' and lockout.

It's actually playing up right now as I type this. You'll see from the Nest app and unit, it's requesting CH. You can hear water running through the boiler, but it isn't fired up but the 'mains on' light is lit.

 

[cuke2u]

It's an S plan system.

The boiler is a Grant Vortex Eco, we both checked the valves - you can hear them opening and closing, and the control arms have free movement.

I'm confused by the boiler manual if I'm honest, in two areas.

1) There's a small light on the switch, the manual says "Wall hung boilers have a ‘mains on’ neon, see Figure 2-2, which lights when the boiler is switched on." and then right underneath that "The ‘mains on’ neon light does not necessarily indicate the burner is firing."

The strange thing is, that light doesn't show when the boiler is turned on and no hot water is being requested.

2) the manual also states the thermostat on the boiler should be equal or greater than the thermostat temperature set on the hot cylinder, but there's no display or marks on the knob that tells you what the boiler thermostat position translates to in temperature.

No overheat light, the only lights are the 'mains on' and lockout.

It's actually playing up right now as I type this. You'll see from the Nest app and unit, it's requesting CH. You can hear water running through the boiler, but it isn't fired up but the 'mains on' light is lit.

Mine too does behave somewhat in a similar fashion, if I turn up the boiler thermostat to it's recommended 'winter' position, about three quarters up, the overheat sensor will trip in, so I run it at around a third up from zero.
When you get the last behaviour you refer to has the boiler already been on for either hot water or a call from a another thermostat? I say this because mine does do something similar also when the SRV's are regulating the radiator temperature. When this first occurred I checked the pipes going immediately in and of the boiler out they were hot thus all that's happening is water is hot enough in the boiler and is just being pumped around the pipework, then there is no need for the boiler to be on, just in it's 'ready state'.
Hope this makes sense to you...