Vokera Syntesi 35 central heating only reaching 50deg

[GazzoH]

Hi,
I have recently noticed that my radiators were not getting very hot, even with the heating control set to max temp. The LCD display on front never shows more than 50 deg when the heating is on and is around 37 deg most of the time but fluctuates up and down quite often.
The DHW works fine and is scorching hot when set to max. From what I can make out from the manual, I need to replace the main PCB. Does anyone out there have any other ideas as to what is going on or even confirm that I need to replace the main PCB? Any advice would be very much appreciated.
The system in question is a Vokera syntesi 35 combi boiler which is around four years old.

Many thanks in advance,
Gary

 

[nickso]

can you set it lower when you turn the CH temp knob down?

 

[GazzoH]

No, does not really seem to make any difference when i move the temp control, it seems to do what it wants! It is sitting at 38 deg at the moment. I have just selected min, medium and max temp. The temp never changed at all during the last 5 min. Thanks for the reply

 

[nickso]

could be the spindle for the CH temp control is broken.

 

[GazzoH]

If it was the spindle, would it not just remain at a set pressure and not fluctuate from around 30 to 50 deg?

 

[Agile]

The spindle operated pots set the target maximum temperatures for the CH and DHW.

The display indicates the value measured by the sensor. On most boilers this is actually the system boiler flow temperature on both CH and DHW but on some Vokeras it is the actual DHW temperature in the DHW mode.

Usually the professionals will have a better idea of the likely cause and understand why that should be the case! A "pressure" is a force per unit area and never a temperature!

Tony

 

[GazzoH]

Yes, I know the difference between temperature and pressure, I meant to type temp, but wrote pressure by mistake.

Can anyone advise any other likely causes of this prob?
rgds,
Gary

 

[Agile]

Can anyone advise any other likely causes of this prob?

Gary

We have told you the most likely cause.

There is only one likely cause.

The other possible causes are unlikely.

Tony

 

[snb]

change the primary thermistor. but for the cost you might aswell change the secondary thermistor at the same time.

a common fault when they reach 4 or 5 years old

 

[GazzoH]

Well Tony, the likely cause is not the cause, the problem must be an unlikely cause then..... Are you a heating engineer with vokera boiler experience or just a keen DIYer? Common sense would point to the issue not being a faulty spindle (You say yourself: The spindle operated pots set the target maximum temperatures for the CH and DHW). I would expect the symptom of a faulty spindle to be the inability to control the temperature, NOT for the temp to be unstable and fluctuate.

Thanks snb, i will look into what you suggest.

regards,
Gary

 

[Agile]

No, does not really seem to make any difference when i move the temp control, it seems to do what it wants! It is sitting at 38 deg at the moment. I have just selected min, medium and max temp. The temp never changed at all during the last 5 min. Thanks for the reply

I would expect the symptom of a faulty spindle to be the inability to control the temperature,

You seem to be giving conflicting information!

Have you actually inspected your boiler to see if the pot is actually turning or are you relying on your "common sense" to make your own deduction that the spindle does not turn?

Are you a heating engineer with vokera boiler experience or just a keen DIYer?

Since my signature says "ARGI Registered Engineer" that might be expected to give you a clue about my profession.

ARGI is the "Association of Registered Gas Installers" and in addition I am registered with Gas Safe which has taken over from CORGI.

Tony

 

[GazzoH]

Conflicting information? Which part of : "The LCD display on front never shows more than 50 deg when the heating is on and is around 37 deg most of the time but fluctuates up and down quite often." is conflicting?
As I said before, adjusting the temp control makes no difference, it continues to fluctuate!
I have this morning looked at both temp control knobs (one of which is working fine on the DHW). There is no difference in their operation. Again, would a faulty spindle not merely prevent temperature regulation and not cause the fluctuation I describe???? Your diagnosis of the spindle from the symptoms I describe did not seem the logical fault to me, hence the reason I asked for other likely causes. I confirmed this this morning.

Gary

 

[Agile]

Have you actually looked at the potentiometers ( not the knob ) to see if the CH knob is turning it?

Tony

 

[GazzoH]

Yes, all three control knobs on the front face panel turn the pot on the main PCB.

Please answer the question: "would a faulty spindle not merely prevent temperature regulation and not cause the fluctuation I describe?"

I am not a heating engineer but have experience with electronics and mechanics, hence the reason I am looking to carry out the diagnosis/repair myself and looking for helpful advice. I am not talking out of my a** and would appreciate friendly, constructive advice from experts on the subject, not derogatory and dismissive cr*p.

To me, a faulty pot/PCB is the most likely cause now. What I am looking for is other possibilities (other than the temp control spindle) or confirmation that I need to replace the PCB. As the PCB is quite expensive, I want to be sure that it is at fault before purchasing one.

Thanks,
Gary

 

[Agile]

Please answer the question: "would a faulty spindle not merely prevent temperature regulation and not cause the fluctuation I describe?"

I am not a heating engineer but have experience with electronics and mechanics, hence the reason I am looking to carry out the diagnosis/repair myself and looking for helpful advice. I am not talking out of my a** and would appreciate friendly, constructive advice from experts on the subject, not derogatory and dismissive cr*p.

Thanks,
Gary

Whilst I am happy most of the time to assist diagnosing faults, I do not give educational essays. You can get them from text books! You seem unable to realise that the temperature will fluctuate under the control of modulation and anticycling delays. I take that into account but you dont need to. Its the too low max temp which is being reached that is your problem.

With your apparent experience of electronics I would have expected that you would not need any help to diagnose the fault on your boiler as its only a simple temperature measurement and control system.

I dont think that what you have written above would encourage anyone to continue to give you "friendly, constructive advice". As the Dragon's Den would say, " I'me out!"

Tony