Oil boiler r8uns but only occasionally fires

have you checked the photocell? They can get sooted up and normally get replaced as a matter of course as part of the annual service.....

Wouldn't that cause a lockout though, as in 'no flame detected' ?

I haven't checked anything yet.

I thought I would ask first...

You could check the call for heat is getting as fas as the boiler to make sure its not a problem with the system controls rather than the boiler.

There is a brief section in the manual:

Page 63 onwards:

Are you able to hear the igniters?

You may also be able to check whether the coil gets volts so that oil is released into the boiler.

If the motor runs properly for 5 minutes and does not light or lock out I would be suspicious of the control box.

that's the odd thing, I don't think I can

Yes...that makes a lot of sense.

Its a riello burner...what do they have?

Does it only do this first thing? I had a fault like that where there was a very slow solenoid valve leak allowing oil to build up overnight.

It would flash off on the first ignition and fail but then work properly after about 15 minutes to recover and then be fine for the rest of the day. The sensor was gradually sooting up as a result but it was a slightly leaky solenoid that was guilty.

I presume you can hear the HT ignition spark? Smell of kerosene?

The Reillo burner I have is an RDB. It has a control box but no separate transformer.

I often see that our thermostat shows the little flame saying it is asking for heat. But the boiler doesn't fire. Moving the slide switch on the thermostat from Auto to Off and back again usually cures this. Poor contact in the relay, I'd say. Might this or something similar be happening to you?

dont have any of that. I cleaned the flame sensor but that didn't work. however it suddenly started on the timer later on with a foul stink of raw kerosene. Maybe it got flooded?

am trying to find a heating engineer who is remotely interested in work

That does sound a lot like the solenoid valve may be leaking oil into the burner jet so that with time off it ends up too wet with kerosene.

I expect they would want to do a full service on it as well as a repair.

RDB sounds familiar

Well it fired up in the middle of the night so I rushed down and turned the UFH on and it ran for a few hours then stopped as it should, and now it wont relight

Of the 5 trustatrader people listed locally, two have replied to say they cant do it. The other three haven't bothered.

Any hints on how you get the mythical 'man in' ?

Try the OfTec website for a list of OfTec accredited local traders?

(I have a a possible contact if you are around the Kidderminster area)

Sadly I aint...

I had an old Firebird boiler with a Riello RDB burner and most of its faults did indeed lead to lockout after up to 15sec. They include a capacitor in the EHT generator, a motor capacitor and the common one of the flame sensor getting too dirty to detect the flame.

I afraid my recollection is a bit hazy, but I think I did have one fault that led to the pump and fan running indefinitely without an attempt at ignition. This was due to the light sensitive sensor failing iin a "flame detected" state, so that the controller became confused and never initiated the spark. I don't remember for sure but I think the sensor is an LDR that goes low resistance when illuminated and mine had failed in a low resistance condition. It is either that or vice versa! Anyway it was the opposite failure to the normal failure to detect the flame,

However, one would expect the combustion chamber to accumulate kerosene until the boiler was turned off so the pump/fan stopped. I can't honestly remember if mine did (I also had a few pump seal failures but these led to kerosene ++ outside the combustion chamber with a working boiler. If my sensor fault didn't lead to kerosene accumulation it may be because of the confused controller not opening the solenoid.

TL, DR try a new sensor, possibly after measuring its resistance with the window covered - I can't remember where I got the spec.

PS. It turns out I have a new spare sensor (and a 530SE controller plus another 530SE which was old but serviceable after capacitor replacement as I recollect)[1]. The resistance in room light is about 18k to 26k depending on how light, and about 380k in the dark. So if it is below, say, 50k with the window occluded it could cause your fault, IME.

PPS The quick test now I think back to my fault analysis is to remove the flame sensor from the control box and put the latter back. If the fault is a low sensor resistance the boiler will go through a normal start sequence, detect no flame (as no sensor) and lock out in the usual way.

Yes, that is exactly what is happening. I finally got hold of a Man who says he can be Got In later tomorrow, and after describing the issue he seemed to know exactly what it was.

The boiler room now stinks of kerosene

It fires up if cold, but not if hot.

I can't honestly remember

The Man will do that, or fit a new control box if that doesn't work, I guess

Coming late to the party but if the boiler is a low level flue version it may have an auxiliary run-on timing circuit which operates the motor and fan to purge the combustion chamber of fumes at the end of a flame demand cycle so in adverse wind conditions the ball of flame and hot gas in the chamber wasn't blown backwards into the burner leading to burnt photocells and stink in the room. These had a failure mode where the motor and fan would run indefinitely but no ignition attempt was forthcoming.