Cold morning start up problem

[Robert Tyrrell]

I'm just curious on this one as I think that I have the answer already but I'd like to be certain.
A customer of mine with an old Trianco Eurostar 125 (External) has had a fault develop in that the boiler won't start first thing in the morning. It always goes to lockout, but when he restarts it, it will run without any problem at all.
I went over a couple of weeks ago and diagnosed a pump problem as the pressure was flicking up and down all the time the boiler was running but haven't been able to get back to replace the pump (I usually keep them on the van but I'd just replaced one prior to getting to his place so needed to re-stock). Whilst I was there I did notice that there were a lot of small air bubbles in the tiger loop and, although I know its an air separation unit, it did concern me as I haven't noticed them before when I've been over to service it.
Sooooo ..... my query is - as its still working, after the initial lock out and restart, and running ok every day, could it be anything else that I might have overlooked?
I was going to post a video of the pump pressure gauge but I keep getting an error message so the explanation will have to do

 

[SimonG]

Over aired.

 

[Best]

+1 for probably over aired.
Or nozzle could be partly blocked creating over aired mix.
If the bubbles very noticeable in Tigerloop, maybe air is being drawn in. Check the oil hoses or just replace them when you replace the oil pump.
You could clean the boiler shell first and then use analyser before you work on burner to confirm if it is high air mix, with low CO2. Although I usually just get stuck in and fit the usual new nozzle and oil pump or whatever else that I know is faulty.

 

[Chalked]

Could be a small leak in the oil line, allowing air to be drawn in when the boiler is off for a few hours.

 

[DaveyHep]

Check your filters. I had this when I had slime in the oil line.

 

[Robert Tyrrell]

Thanks guys, got to the site and noted that there were builders working away so just to be safe, I went over every joint and made sure it was good and tight.
Changed the nozzle and the pump pressure shot right up, off the scale, and it wouldn't adjust so it was replaced and the combustion settings checked - smoke 0; CO2 11% pump pressure at 115psi air at 5.
Seems to be working now, and just a few small air bubbles in the tigerloop

 

[SimonG]

Glad you got sorted.

I would have it a bit lower than 11 on the co just because of the age of the unit.

 

[Robert Tyrrell]

Glad you got sorted.

I would have it a bit lower than 11 on the co just because of the age of the unit.

Yep - I would normally but I just couldn't get it to go lower in the time I had. Needed to make a 35 minute journey afterwards, collect the better half, and take her for a medical appointment.

 

[SimonG]

Was it a conventional flue?

 

[Robert Tyrrell]

External unit with balanced flue