My Vokera Excell 80SP's Weekend

[rednaxela]

4 weeks ago, 10 year old boiler moved from downstairs to upstairs due to pending extension, All ok.
last week, DHW started going hot, then cold in loops.
Friday morning, system operating normally with steady DHW,
Friday night, fault returned.
Saturday Morning 8am, Idle fan was off!, only sign of life was pilot light.
Turned on DHW tap, with a splutter, boiler and fan burst into life, but no flame start.
Tried for few hours on and off, then boiler returned to its cold hot DHW fault (sometimes from cold, it would take up to 20 seconds
from pump starting to flame lighting)
With stat turned down, the hot cold fault would be warm, cold. With the stat turned to max, the water would be very hot, cold.

Sunday, boiler seemed normal first thing, but then cold hot fault returned.

Central heating operating normally each time tested. Idle fan has not found to have stopped again. (new flu was fitted during move)

Corgi man says its CH heat exchanger effecting DHW, but I think it could also be the PCB due to fan stopping?? (all connections checked)

Question a: does this sound like heat exchanger + PCB?

Question b: Would value your opinion, should I get it repaired (£220 HE/PCB +lab) or is it time to replace with Ideal Mini HE (£600 +lab)?
I was told that it is a big risk moving an old boiler..

As always, your opinions will be gratefully received...
thanks Alex.

 

[Agile]

I think that you have two faults but neither is the PCB.

Nor do I think that your CORGI person is very good at fixing boilers!

Its cheaper to buy your Mini HE under the original manufacturer's brand rather than badged Ideal !

Tony

 

[rednaxela]

What do you think the faults are?
who makes the mini HE?
thanks, Alex.

 

[simond]

I think its a Biasi.... unless Agile knows better.

 

[scatmanjohn]

What do you think the faults are?
who makes the mini HE?
thanks, Alex.

Hot, cold water fault sounds like an air flow problem (very common on these) Get your Corgi fella to remove the fan and clean the venturi (with a small file), clean the fan and lubricate it. Also while he is at it get him to wash the main heat exchanger it will be caked up to hell.

The slow fan fault is usually either the boiler flow microswitch (or just the flow switch not returning to its rest position) or the slow fan resistor.

Forget buying a new boiler you have already got a decent one.
What you need is someone who knows how to fix boilers.

 

[Agile]

The slow fan resistor rarely fails itself but more often gets so hot that it melts the solder on its connections and they fail.

Easy enough to resolder if you remember to put out pilot light and disconnect the power.

Ideal Mini C are rebadged Biasi boilers and dont include the timeclock as standard.

Tony

 

[scatmanjohn]

Agile wrote:

The slow fan resistor rarely fails itself but more often gets so hot that it melts the solder on its connections and they fail.

correcta mundo, However funnily enough as coincidence would have it i found one today that had failed.

 

[rednaxela]

Firstly, thank you all for your help.
I have found it very interesting trying to figure out what is wrong with my boiler, and to run my thoughts and also things I have been told by my plumber past a larger group. I have certainly learnt lots this week.
(just wish one of you was near Great Yarmouth)!! 8o)

I will get my man back to check out the fan. I know that the casing has not been removed since the move, so I guess all manner of things could have fallen into the pipe. The fan has only stopped twice so far.
I am an electronic engineer, so I will see if I can find out exactly how the slow fan gets its power.
I did find another post about Excell 80SP's from last year. From reading that, my hot water fault does look as if it is the DHW heat exchanger (the fault in that post was exactly the same as my boiler).
My corgi man told me he would rather replace than clean, so I am not sure which way to go at the moment.

Thanks again for your continued support. I really appreciate it.
You guys have convinced me that there is still some life left in my old boiler....
Alex.

 

[Agile]

If the slow fan stops then it is likely to make the HE connections leak.

I suggest you check the fan and series resistor yourself.

Your man may not know how to clean the HE or just wants to bump up the price. I dont think the main HE is at fault!

Tony

 

[scatmanjohn]

The fan has only stopped twice so far

If its intermittent then it is more than likely a flow switch problem.

 

[rednaxela]

Hi..
I carried out a visual inspection of the slow fan resistor. One of the wires was hanging on by a tiny piece of plastic sleeve! The other one seemed better, but I removed the resistor anyway. Its value was ok, so I cleaned up the terminals and re-soldered the wires. I had to cut back and clean the wires as they were very tarnished due to heat I guess.
Switching everything back on, I could not believe how hot it got! Even the wire was warm up to 5cm away! is this normal???

The resistor didn't even have any heat compound between it and the case. can anyone think of a reason not to put a little on? I would have thought it would help with the dissipation.

I am also wondering if the resistor would be hotter if the fan had to work harder. I am still thinking it may be worth while checking the fan for obstructions.

Anyway, hopefully all that remains is to get my corgi man in to do the hot water heat exchanger.

I must thank you all again for your help so far!!

Alex

 

[scatmanjohn]

rednaxela wrote:

Anyway, hopefully all that remains is to get my corgi man in to do the hot water heat exchanger

Why?

What tests has your CORGI guy carried out to prove that its the DHW heat exchanger?

None is my guess.

I've already said what your first port of call sould be. (fan venturi)

 

[rednaxela]

hhmm, he didn't do any tests apart from run the boiler. + this morning, the Mrs turned the hot tap on for a few seconds and after that..... the fan stopped.
I then ran the water for longer to let the boiler kick in. Following this the fan started again.
"oh poo" was my comment! as I was sure the resistor had fixed it. 8o)

I will look at the fan venturi after work. I'm a little confused on what to do with it. I guess check the flexible hoses, but how can I check the actual sensor?

Thanks, Alex.

 

[DP]

While venturi can result in boiler rapid firing, a prolonged cycling could be result of system muck now sitting in the HW heat exchanger.

Heat produced in the main heat exchanger will be used to heat the cold water flowing in the secondary heat exchanger. If the cold water flow rate within the plate to plate HE is as specified (9.8 for 80,000 btus) , HW stat is at max, cold water from the mains is at 10 degree C, the water at the hot tap will be at 45 degrees C. Under these circumstances, burner is unlikely to modul;ate as it is working flat out.

Reduce the flow rate or reduce the HW stat setting, burner will modulate to mainatin equilibrium.

If this boiler (like any other boiler with plate to plate secondary HE) has been fitted to a dirty system, you can rest assured the muck in the rads will eventually come to reside in the HW heat exchanger. When this happens, the HW HE fails to use up the heat produced by the main heat exchanger due to REDUCED FLOW RATE on the primary side caused by the muck in the HW HE. Net result is boiler does not modulate but goes from full on to full off. Water from the hot tap starts to cool down as primary loop heat is used up. Soon the control decide to fire the burner and temperature rises and the cycles begins.

Cold air is heavy. Burner fires and cold air loses its 'weight' as it is heated rapidly. Air pressure switch releases due to lack of pressure as a result of deposits in the venturi. Very simple test to check for this.

It is not uncommon for the restrictor ring to be left in place on long flues. I would check on this also.

 

[rednaxela]

Gave the Venturi a visual. The pipes were clean, and the relay clicked in and out with a slight blow on a pipe.

The fan was very free and was taking around 20 seconds to stop once turned off. Connections seemed ok.

I can't get the fault to occur when I test it out!

All I can think of is a faulty microswitch that the DHW activates..?