HRM Wallstar Oil Boiler - Advice please

[Sausage_Hider]

Hi all,


I have a Wallstar Oil Boiler 12/15.

A few years ago, it developed a problem where it would fail and it required a manual reset on the boiler controller outside.

I didn't know much about oil boilers back then.

I have had a number of 'heating engineers' and so-called specialists to it but so far none have cured the problem.

I decided to figure out how these things work for myself to give me a greater understanding of what is going wrong.

So, this is what happens.

When there is demand for heat, the boiler from cold (in a none failed condition) fires up without the slightest problem.

It runs to get the water hot, shuts off, starts again as water cools etc... normal running.

Then, for no apparent reason, say after 30 mins or 1-hour etc, it will fail to ignite. This triggers the fail and requires a reset on the controller.

Sometimes the reset will work and the boiler will fire up and continue, sometimes it will just keep failing.

If I leave it to cool down for a few hours, it will generally fire up as normal (after clearing the fail with the reset).

It seems that when the boiler is very cold, there is no problem. If it is also very hot, it doesn't seem to be a problem, but in-between is where it fails.

The engineers etc have changed the nozzle, plastic pipe, solenoid, controller and filters and the problem persists.

Now then, things I have checked.

When starting, the pump runs (pulsing of the oil can be seen in the clear pipe). It does its 10-15 second purge then the solenoid clicks and the oil flows, boiler lights.

All good.

When it fails, it NEVER fails when running, only on re-starting during the normal heating cycle.

It goes through the normal procedure as above, solenoid clicks open, oil is seen to flow and then within about 3 seconds it shuts off with the fault.

Now, as I can see the oil moving, it isn't the solenoid, it’s not air as I can see the oil in the line, it’s not a blockage as again I can see the oil moving in the line.

It seems to be the igniter.

I have had it apart, cleaned the electrodes, checked the gap 3mm+-0.5mm and level with the top of the nozzle.

It's not the flame detector because when it fires up, you can hear it ignite and it doesn't get that far.

Does anyone have any experience with this same fault and how was it cured?

Could it be the transformer (that creates the spark), the leads to the electrodes or the electrodes themselves.

Puzzling as it only fails when the boiler has been running. The temperature in the burner cabinet is always quite cool, but the fault is definitely heat related!

This must be a known problem, on my street 12 houses, we all have the same boiler and 7 of them have the exact same problem.

Surely someone must know what the problem is.

Oh, the boiler is about 12 years old.

Thanks.

Martin

 

[SJB060685]

With all the parts you've had engineers randomly change you could of bought a new burner. That's another option, many decent engineers have spare burners for problem child situations like this. Maybe if they have a sound Sterling that could be fitted for a week, at least then you'll know if it's a fuel or burner problem. If that's not an option then they need to go through what I've said to rule out possibilities. If I attended and couldn't find the fault first time, after replacing the pump as you said was then I shouldn't be charging you for return visits

 

[John.g]

Any remotely operated fire valve in the oil supply that maybe throttling it?.

Oh yes, I see you had it replaced.

 

[Simonvr46]

left heating engineer a voicemail on Monday morning and tried ringing him during the week. Not heard anything. Haven’t paid anything yet so I know he’ll get back at some point.
Boiler still playing up.
Yesterday morning it wouldn’t start, tried several times ended up bleeding oil line and it started.
Yesterday afternoon wouldn’t start, again tried several times. Tried bleeding oil line again but still wouldn’t start even with 2 inch air bubble. Left it 10mins and it started.

 

[John.g]

Think you will have fit that oil pressure gauge and monitor after cut out.

 

[SJB060685]

The pump has recently been replaced and I'm assuming the coupling along with it and seeing as it's the same problem before and after I'd suspect neither are the issue. Obviously all air needs to be removed from the pump for reliable ignition, a gauge usually fluctuates with air in pump. The motor is running and assuming the coil is sound and clicks then atomization of fuel at nozzle needs to be checked along with spark. If the pump is producing operating pressure and coil opens but no fuel out of nozzle then it could be a dodgy nozzle, a blocked/partially blocked HP line or a dodgy NRV (although I'm not sure if the Sterling has one). If you have neat fuel out of nozzle next check is spark.

 

[Simonvr46]

Never did get to the bottom of this issue.

Decided rather than spend/waste money on trying to fix it.

We’ve gone down the route of having a new boiler, I purchased Worcester Greenstar heatslave II through staff discount scheme we have where I work and then paid an accredited Worcester installer to install and commission boiler.

It’s been installed 11 days and no problems at all. Starts every time and we now have constant hot water.

 

[SJB060685]

Thanks for updating us. Im sorry to hear you made that decision, although it does suggest the problem was never fuel related and was within the burner, unless the installer rectified a proper when installing.
Not a fan of combi boilers personally but if I remember correctly there's just the two of you and they are decent boilers.

Again thanks for updating us.

Many thanks, Simon

 

[Simonvr46]

Thanks for updating us. Im sorry to hear you made that decision, although it does suggest the problem was never fuel related and was within the burner, unless the installer rectified a proper when installing.
Not a fan of combi boilers personally but if I remember correctly there's just the two of you and they are decent boilers.

Again thanks for updating us.

Many thanks, Simon

Hiya, only things that have changed regarding the fueling are that the boiler is now sat on the floor rather than it being in the wall so that the pump doesn’t have to lift the oil up and the fire valve has been replaced with new one instead of the HRM version with non return valve. The installer let me take off all the parts that had been replaced, which I thought was decent of him as he could have kept them and used them.

I think we will use less oil especially during the summer as both of us are at work and we have boiler set to only come on in morning and evening to give us hot water When we need it, instead of it being on all the time and keeping the heatslave tank at constant temp.
Thanks for all your help.

 

[John.g]

Thanks for updating us. Im sorry to hear you made that decision, although it does suggest the problem was never fuel related and was within the burner, unless the installer rectified a proper when installing.
Not a fan of combi boilers personally but if I remember correctly there's just the two of you and they are decent boilers.

Again thanks for updating us.

Many thanks, Simon

SJB, you may have a few comments to make re Stored combi boilers output and flow rates, there are numerous queries on here re gas combi flow rates as well.

I am looking at a brochure for a Firebird C35 combi boiler and to quote "D.H.W. Guide Performance in litres/min (120 litre draw-off at 40C deltaT) 20". It has a primary store of 40 litres heated to 78C.
Do you know if this guide performance is typical for oil fired combis? and also how is this number of 120 litres arrived at?
My simple calc shows that if one assumes cold water at 10C, then with a deltaT of 40C the stored cylinder will give a volume of 40*(78-10)/(50-10), 68 litres at 50C (which should give 20 LPM but only for 68/20, 3.4 mins, the burner should kick in at 73C and then the 35kw boiler will give a continuous flowrate of (35*860)/(40*60), 12.54 LPM.
My main query is this 120 litre figure?, the flow rates are simple to understand IMO.

 

[SimonG]

120 litres to fill a bath. They want to give the idea that you can fill a bath before the store gives out. It doesn't last though.

 

[SJB060685]

Its to do with the amount of stored energy in the thermal store. 120 litres is what can be provided at that delta until the store depletes.
Gas is different, they ramp up to full output and can modulate down for the lower load of CH.
Because up until recently domestic oil burners are fixed rate they have to use a store to aid in HW production.
If my understanding and maths is correct then 20 litres per minute at a delta t of 40°c would require an input of roughly 50kw but as said above if there was no thermal store and you had a nozzle size and pressure to input 50kw for HW then the CH side will also have the same input, obviously being massively oversized.
Perhaps when fully modulating oil burners take off there will be no need for a thermal store.
Thats my understanding, if I'm wrong then please correct me.

 

[John.g]

My calcs show that a 70 litre store would be required to give that 120 litres, the store is definitely required as you say because of the fixed boiler output and if you only needed a flow rate of 4 or 5 LPM then the boiler would be constantly cycling on/off. A continuous 20 LPM at a deltaT of 40 requires 56kw, the more normal quoted deltaT of 35C would require 49kw.

 

[SJB060685]

Can you break down your calculation method.
Bare in mind as the store temp decreases the burner will engage and supply additional energy, until a certain point where the input cant match the output.