Grant Combi 90 MKII Issue - Any help or advice greatly appreciated!

[DabHandLuke]

We have the above Oil Boiler. Had a selection of new parts fitted over the last 12 months (see below). Everything has been running fine for about 6 months since last repairs.

Over the last couple of weeks, any time the CH is switched on, it fires and heats as it should but once the heating is on for more than 45min - 1hr, the control unit trips to red. Everything else appears to work fine, hot water no issues. I checked the expansion vessel, it had failed (full of water) replaced this assuming that was the obvious issue but the reset problem still persists.

Any advice before I spend yet another chunk on getting this investigated. It's been a cash hungry boiler over the last 12 months! Some expert advice or suggestions would be wonderful. Thanks in advance.

Parts replaced recently:

New Digital Control Unit - 12 months ago.
New Heat exchange - 6 months ago.
New Divertor Valve - 6 months ago.

 

[Hairymelon]

Do you mean the burner locks out? Or is it the overheat thermostat tripped ?

 

[DabHandLuke]

Hi, Thanks for the reply, apologies for the slow response, late shift!

Once the heating is switched on everything works for around 45 minutes then the Red Light illuminates on the control unit and the heating shuts off. If I reset by pressing the Red illuminated reset switch, the boiler fires up again as normal but the same issue results if I restart the central heating again. Obviously, as per the "Reset twice only" warning on the burner casing, I'm avoiding using the Central Heating after it trips.

Sorry if any of my description is confusing, far from an oil boiler expert! Although my servicing level has improved greatly since I inherited this boiler 4 years ago! I'm likely going to call an engineer by the weekend, heavily pregnant partner who does not currently have the tolerance for the cold (praise be for the log burning stove!) Would be great if any of you fine experts could potentially diagnose/suggest an obvious/potential and ultimately cost reducing fix before I call out the engineer however! Many thanks in advance!

 

[oilhead]

What burner do you have fitted to this boiler? Your mention of a digital control unit suggests that the burner has been replaced from the original Riello G5.
Your fault suggests a failing oil pump solenoid coil. A cheap part and easy to replace, but you need to know which burner you have.

 

[snb]

i'm guessing it still has a G5 but he is referring to the red light on the control panel. pump solenoids rarely fail on riello's so i would be looking at fuel starvation. I would check the filter at the tank is clean first.

 

[DabHandLuke]

Thanks for the input gents. I've added some photo's of the burner for clarification. I think it is the original one but couldn't be sure as we inherited it around 3 years ago. I'll defiinitely check the filter at the tank. It was replaced a couple of years ago but doesn't seem a difficult job to access or clean. Fingers crossed it is that as this would certainly be an easy and cost effective solution! Any other advice or suggestions will be greatfully recieved.

*UPDATE*
Checked the tank filter. All clear, no debris inside housing, filter looks clean and in good shape with oil flow as normal.

 

[oilhead]

This is an RDB burner and is a replacement for the original. I still think, for what it costs, replace the solenoid coil on the fuel pump. This can be done without removing the burner and it is straightforward when you look at it. Just be sure you refit the steel horseshoe shroud. Riello coils are more reliable than Danfoss, but they do fail.
For examples of supply check ebay or Amazon.

 

[Hairymelon]

Another ‘clairvoyant’ opinion by myself , I’d get an oil boiler guy to remove and check how the oil pump feels when rotated as they can become semi seized when warm and also to check the capacitor. The solenoid coils are operating at 35v dc so rarely fail, but if they do, the burner motor runs continuously without firing or locking out

 

[DabHandLuke]

Thanks for all the advice everyone. After closing both valves and checking the filter on the oil tank, the boiler now refuses to even reset, red light straight away. So possibly it is a fuel flow issue afterall, pump or similar. I've got an engineer coming out today so hopefully back in the world of heating real soon.

 

[oilhead]

If you have been repeatedly pressing the reset button, you may have goosed the control box. Totally isolate all power from the boiler for 1/2 hour then see if it resets.