Suprima 80 short-cycling - suspect faulty 5111603

[davidr]

Hi

My suprima with the new PCB kit intermitently cuts out after about 4 to 8 minutes of running then goes through the auto reset sequence before restarting. A rapid flashing red led (4 per sec) is shown which I think means air pressure failure - fan stopped. Water temp at the pump gets to about 65 deg C.

The fan, flue, air pressure switch pump and everything else are fine. Venturi is not blocked, no crap in fan, tubes all fine and new air pressure switch. The rads are 10 years old with little sludge and get very hot.

Everything works ok apart from this short-cycling that's wearing out my gas valve and wasting gas !

The boiler has had this problem for a couple of years but it comes and goes - always seems worse around Christmas when CH on all day

Is this likely to be a bad PCB ? anything else I can check before I buy a 2nd 5111603 and 4th pcb for this bloody boiler !

Thanks
David

 

[gas4you]

Is the pump continuing to run when the boiler shuts down? It should for approx 5-6 mins.

 

[davidr]

Thanks Dave

The pump continues for about 30 seconds to 1 minute after the boiler has cut out - long enough for me to run from downstairs utility to upstais a/c and monitor it running for a few seconds !

From cold, I set air thermostat to max, advanced boiler programmer to continuous. Boiler fired, ran for about 8 minutes getting water at pump to 50 dec C before cuttting out, starting auto reset sequence and re-firing.

The cut out at the suprima is sudden stop - like a power failure - everything cuts out, led goes orange than flashes green/orange but fails to light. I don't hear the APS open and I get the rapid red flashing led before the auto reset sequence starts and the boiler relights.

I think the pump would continue for longer but stops due to the auto reset sequence.

I'm pretty sure this isn't the APS - I've changed it for a new one and cleaned the tubes.

 

[lloyda]

My Suprima 100L has a flow switch in series with the APS. The last engineer to work on my boiler said the flow switch was not fitted to all models. Might be worth checking yours.

 

[davidr]

My suprima 80 doesnt have a flow switch and there's none fitted - only the APS connected - thanks anyway

 

[Agile]

Can you measure the flow and return temperatures at the boiler ?

This information might indicate a flow problem.

Its surprising mow many faults can be identified by a simple thermal survey which very few professionals bother to do.

Tony

 

[davidr]

Hi Agile

Using clamp-on dial thermometers I see 60 deg C at input to pump (about 5 meters from flow side of boiler) and 45 deg C at a tee drain off cock directly above boiler and connected to return pipe (closest I can get). Pump is running on "speed 3" and I have 16 rads of different sizes and types on 10mm microbore with a hall 15 mm bypass rad. All rads have TRV's (except hall rad) and all get very hot.

Could the thermister have failed or the overheat thermostat?

 

[gassafeman]

get an RGI to check the Gas Valve.

 

[davidr]

thanks Gassafeman

The gas valve was replaced 18 months ago for a new part and was fitted by a CORGI boiler specialist. Is it time to call out Heat Team or BG?

 

[Agile]

I am not confident that your temperature measurements are very accurate. If they were it would indicate a too low flow rate as the differential across the boiler of 11°C.

Did this "CORGI specialist" set the new gas valve to the manufacturers specifications?

Many dont know how to or think it comes preset in the box! ( They dont! )

I always advise RGIs to remove the sensor and add thermal transfer paste to ensure its well bedded.

Tony

 

[gas4you]

Whats wrong with 11C? It's a standard differential for non condensing boilers such as what the OP has

 

[ChrisR]

YOu could measure the gas consumption rate - see the FAQs.

Does the boiler stay on longer if you've got it coolish, them turn the temp knob right up?

COuld you have a partial air lock?

 

[davidr]

I am not confident that your temperature measurements are very accurate. If they were it would indicate a too low flow rate as the differential across the boiler of 11°C.

After some time the boiler starts to work correctly and shows 70 C at pump and 45 C near return. I suspect the 45 is low but because of boxing above boiler I cannot get a thermometerany closer.

Did this "CORGI specialist" set the new gas valve to the manufacturers specifications?

Yes - initially he set it too high but then reduced it to the lower rating for Suprimra 80 as shown on the boiler spec label.

I always advise RGIs to remove the sensor and add thermal transfer paste to ensure its well bedded.

Thanks Tony - but which sensor is this? Do you mean thermister that pushes into the cavity in the flow tube?

 

[Agile]

After some time the boiler starts to work correctly and shows 70 C at pump and 45 C near return. I suspect the 45 is low but because of boxing above boiler I cannot get a thermometerany closer.

I always advise RGIs to remove the sensor and add thermal transfer paste to ensure its well bedded.

Thanks Tony - but which sensor is this? Do you mean thermister that pushes into the cavity in the flow tube?

When it is operating correctly the temperature differential is a design value of 11° so with a flow of 70° the return should be 59°. That indicates a flow rate of less than half of the correct value.

There is only one temperature sensor on the Suprema.

Tony