Adjusting AGA Oil Control Valve Min Flow Rate

Firebirdfan · 12 May 2024

Hi, After getting great success from this forum regarding fixing my very old Firebird boiler I was hoping that someone might be able to recognise the valve on my AGA that is at least 35 years old. I want to adjust the min flow rate as it is still running too hot at the lowest setting. When I had it professionally serviced (again for the first time in 30 years) the engineer said that the screw was the rusty one just beside the control know (with a red mark in the photo) and to turn in anti-clockwise. I have turned it 180 deg but the is no change and it is very stiff. Looking at a photo I took when the cover was off there appears to be a much more likely candidate in the silver screw that is resting on the rusty lever that is attached to the rusty screw. I have looked at loads of BM valve photos and manuals but cannot find one relating to this valve. Does anyone recognise the valve and if so could you let me know the name of the valve and which screw I should turn (and in what direction) to make the AGA run cooler at its lowest setting. Many thanks in advance. Michael

oilhead · 12 May 2024

Before messing with screws, measure the flow rates. The data plate on your Aga will give the correct values for your cooker. I always remove the carbon leg and loosen the flow elbow so that it can be rotated out of the door, refix the carbon leg and switch on the fuel, allowing it to drip into the meas uring cup. Let it flow for two minutes to stabilise, then run it into the measure for 2 minutes and divide the amount by two to get the minute output. Depending on your Aga model it will be between 3-7cc for a basic cooker and 6cc for double with a boiler You should also confirm that the oildepth is correct in the burner. Before turning anything, what do you see when looking through the sight glass. Do you have flame above the rings? Remember you need to give a hot burner about 10 mins to stabilise after each adjustment. When lighting a cold burner, give it about 4 hours to warm the cooker up. Excessive flue draught can also cause overheating so make sure you have the draught diverter fitted correctly.
I always recall the technical help people at Anglo Nordic telling me the biggest problem with these control valves is the failed nut on the end of the screwdriver!
Your valve looks like a BM, and the adjusting screws will be the two at the circumference of the knob. You need to put the knob in the low position and then make your adjustments if needed after checking the flow rate. With the top off, you will be able to see the metering stem being pushed down or allowed to rise.
Remember, nothing is instant on a vaporising burner.

Firebirdfan · 12 May 2024

oilhead said:
Before messing with screws, measure the flow rates. The data plate on your Aga will give the correct values for your cooker. I always remove the carbon leg and loosen the flow elbow so that it can be rotated out of the door, refix the carbon leg and switch on the fuel, allowing it to drip into the meas uring cup. Let it flow for two minutes to stabilise, then run it into the measure for 2 minutes and divide the amount by two to get the minute output. Depending on your Aga model it will be between 3-7cc for a basic cooker and 6cc for double with a boiler You should also confirm that the oildepth is correct in the burner. Before turning anything, what do you see when looking through the sight glass. Do you have flame above the rings? Remember you need to give a hot burner about 10 mins to stabilise after each adjustment. When lighting a cold burner, give it about 4 hours to warm the cooker up. Excessive flue draught can also cause overheating so make sure you have the draught diverter fitted correctly.
I always recall the technical help people at Anglo Nordic telling me the biggest problem with these control valves is the failed nut on the end of the screwdriver!
Your valve looks like a BM, and the adjusting screws will be the two at the circumference of the knob. You need to put the knob in the low position and then make your adjustments if needed after checking the flow rate. With the top off, you will be able to see the metering stem being pushed down or allowed to rise.
Remember, nothing is instant on a vaporising burner.

Hi Oil Head,
Thanks for the comprehensive reply. However the engineer checked the flow rate and adjusted to screws to the AGA specified high and low rate. Unfortunately this low rate is still too high so all I need to do is adjust the low rate screw so that less oil flows when it is set to 1 (or below). You are quite right the adjustment screws are at the circumference of the knob, on a more modern BM valve, and I have seen loads of photos/diagrams of this valve. This is not the same valve as it has a screw (accessible through the cover plate) in a different position to the modern valves. If it is this screw then would a drop of WD40 or similar be advised as I do not want to shear this screw. Cheers Michael

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Adjusting AGA Oil Control Valve Min Flow Rate

Firebirdfan

oilhead

Firebirdfan

DIYnot Local

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