HRM Wallstar 15/20 oil boiler cutting out

[magnusflett]

I have an HRM Wallstar 15/20 boiler that is cutting out once or twice a day. It has a bubble in the oil pump suction hose. I have replaced the nozzle and oil filter element recently and checked and sealed joints in the suction pipe but bubbles still enter the transparent hose. In the past air had been sucked in through the filter bowl seal. Since then I changed the filter assembly. I suspect that air could be sucked in along the spindle of the fire valve/non-return valve. Could I be barking up the wrong tree? Could it be an ignition fault? It is a problem that has happened before and has come back to haunt me. Another factor is that the fuel level in the oil tank is low at the moment and could be affecting the boiler. Any ideas anyone?

 

[SJB060685]

I have attached an image above. In the right green rectangle is where I’d suspect a possible suction leakage. The bottom left green triangle symbolises the recommended minimum fuel level. These pumps are capable of lifting fuel roughly 2.5m from lowest level of fuel line. if this is a problem you’ve encountered before then what fixed it last time? Really you should try and an engineer out, there’s only so much a DIYer can do

 

[magnusflett]

Thanks for your informative reply. The boiler was installed in 2006 and has suffered from cutting out at times. Earlier problems were caused by air being sucked in past the O-ring seal at the top of the oil filter bowl. The oil filter bowl was changed as the sealing surface of the filter bowl was porous. (a common problem with aluminium castings). A blocked fuel filter has caused the boiler to cut out in the past after the oil tank was replaced and moved. The tank is closer to the boiler now. Currently, I can see small bubbles drift up into the clear hose.

I measured the oil level as 250 mm from the bottom of the tank. The tank is being filled tomorrow so it will be interesting find out if that makes the problem go away for several months.

 

[SimonG]

When was the last time an analyser used on the combustion?

 

[SJB060685]

Thanks for your informative reply. The boiler was installed in 2006 and has suffered from cutting out at times. Earlier problems were caused by air being sucked in past the O-ring seal at the top of the oil filter bowl. The oil filter bowl was changed as the sealing surface of the filter bowl was porous. (a common problem with aluminium castings). A blocked fuel filter has caused the boiler to cut out in the past after the oil tank was replaced and moved. The tank is closer to the boiler now. Currently, I can see small bubbles drift up into the clear hose.

I measured the oil level as 250 mm from the bottom of the tank. The tank is being filled tomorrow so it will be interesting find out if that makes the problem go away for several months.

Once the oil tank is filled check to see if you're still seeing bubbles pulled up into the clear hose. If you still are then this suggests either a suction leakage or possible partial blockage, a vacuum gauge will help there. Many things can cause gases being separated from the oil if the vacuum was too high, ranging from too high a lift, blocked/partially blocked filters, crimped pipes, even the oil being too cold can cause this. Really you need to get to the bottom of the air/gases being pulled into the pump first.

 

[magnusflett]

Since the oil tank was filled on Monday the boiler has been working without cutting out so the problem would appear to be in the pipework between the oil tank and the oil pump. I will try to measure the pressure/vacuum at the oil tank, 2nd oil filter and oil pump suction hose.

 

[SJB060685]

Since the oil tank was filled on Monday the boiler has been working without cutting out so the problem would appear to be in the pipework between the oil tank and the oil pump. I will try to measure the pressure/vacuum at the oil tank, 2nd oil filter and oil pump suction hose.

From what you've said I suspect the problem was too low oil level, hence the original image I shared. Modern day pumps are capable of lifting oil quite a distance, even Riello pumps can lift a few feet but all pumps have a suction capacity. With your oil level low as it was and only atmospheric pressure on the bottom few inches then low pressure above the oil fill line will be quite drastic most likely causing these bubbles you saw being drawn into clear hose. When an oil line is subject to around 0.4-0.5 vacuum this is enough to pull gases from the oil which in turn make their way to the pump and you have nuisance lockouts.
If the burner is running fine then leave it be, dont start messing around with pressure and vacuum gauges.