Ferroli Optima 701 intermittent DHW

[karlitop]

Hi,

A newbie looking for a little help/advice please.

I have a Ferroli Optima 701 and it seems to have a problem with intermittent DHW. The British Gas engineer has been out and has changed a couple of sensors, (CH temp and 88oC limit sensor) but the fault still persists. He has also cleaned out the venturi to no avail. Initially the loss of DHW was only apparent when the CH was on. BG suggested a build up of scale in the heat exchanger which was causing it to retain head and trip the limit stat @ 88oC. However, recently, the DHW is now running hot then cold in cycles even though the heating is off and the temp gauge reads a low reading.

When I switch the hot tap on, I can see the boiler firing up then after approx 60 seconds, the boiler flame extinguishes and the water runs cold. After approx 20seconds, the boiler re-ignites and the water runs hot. This continues in cycles and is more apparent when the boiler is warm (well warmer than cold).

Does anyone have any ideas? Is it worth getting the heat exchanger de-scaled (not covered by BG) or could the fault be with something else?

The boiler is 17 years old and has served me well, I'll be sorry to see the old girl go if a replacement is in order.

Many thanks

 

[combiman1]

Hi Karlitop just read your posting re ferolli optima 701
you say that the Central heating sensor and the limit sensor has been changed BUT DID HE CHANGE THE HOT WATER TEMPERATURE THERMISTOR ? on the 701 there are 2 temp thermistors 1 for c/heating and 1 for hot water the symptoms you describe are spot on for a Faulty hot water sensor fault the thermistor is basically a variable resistor which monitors the water temperature when the tap is running when the water is getting hot the resistance drops and causes the gas valve to modulate DOWN in pressure to keep the temp constant BUT!IF THE TEMP THERMISTOR ON THE HOT WATER IS FAULTY it telss the electronics that the hot water is too hot and TURNS THE GAS OFF until it runs cool and then the boiler refires and it starts all over again If your Cenral heating radiators work with NO problem then what i have described is definatley the action you need to take Scale i dont think so if your boiler was scaled the water would dribble out of the hot tap it has been many many years since i saw a scaled up ferolli i hope this helps you with your problem I too am a newbie here and this is my first reply good luck regards combiman1

Hi,

A newbie looking for a little help/advice please.

I have a Ferroli Optima 701 and it seems to have a problem with intermittent DHW. The British Gas engineer has been out and has changed a couple of sensors, (CH temp and 88oC limit sensor) but the fault still persists. He has also cleaned out the venturi to no avail. Initially the loss of DHW was only apparent when the CH was on. BG suggested a build up of scale in the heat exchanger which was causing it to retain head and trip the limit stat @ 88oC. However, recently, the DHW is now running hot then cold in cycles even though the heating is off and the temp gauge reads a low reading.

When I switch the hot tap on, I can see the boiler firing up then after approx 60 seconds, the boiler flame extinguishes and the water runs cold. After approx 20seconds, the boiler re-ignites and the water runs hot. This continues in cycles and is more apparent when the boiler is warm (well warmer than cold).

Does anyone have any ideas? Is it worth getting the heat exchanger de-scaled (not covered by BG) or could the fault be with something else?

The boiler is 17 years old and has served me well, I'll be sorry to see the old girl go if a replacement is in order.

Many thanks

 

[karlitop]

Hi Combiman1, Many thanks for the info and quick reply. I've just ordered a replacement DHW thermistor and I will fit it this week. I'll let you know if this fixes the problem (fingers crossed).

Thanks for the tip on the scale too, the hot water runs well (albeit cold)and we have no problems with flow so I think I can rule the de-scale out .

Cheers,

Karlitop.

 

[karlitop]

DHW thermistor solved the problem - thanks for your help!

 

[combiman1]

DHW thermistor solved the problem - thanks for your help!

Hi karlitop glad my advice helped you regards combiman1

 

[leroyman]

Hi i have the same problem, i've had both thermistor sensors changed in the past. DHW gave same problem as poster but CH was running at max when on.
I now have no hot water again and suspect the DHW sensor has gone.

A family member usually does our gas stuff, buts hes no longer available. I know the part is cheap but how much for a call out Staffordshire region.