Advice? -Ferroli 701 heating turning off/on?

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bilabonic

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Hi all

My trusty Ferroli 701CH is switching on /off.

I checked the LED status and done a few basic with my multimeter checks and it’s tripping on the CH limit stat/over temp on heat exchanger.

Would the CH flow temp cause this as it’s not adjusting/modulating the gas valve?
I have tested it’s resistance and it seems ok and within range??

Is the gas valve adjustable or just on/off as I suspect?

Cheers
 
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The thermostat on the boiler to set the CH is also ok.
But even when I have it set at at its lowest in order to call for CH the outlet pipe is gets absolutely red hot.
I can not keep my hand on it!

It’s the internal ‘heat exchange limit thermostat’ (50 on diagram) that is switching the boiler even at its lowest setting.

Any ideas?

Thanks
 
I have replaced the the CH flow sensor (34) but it will not fire at all then?

It is reading approx 1.2k!!! At room temp??
I had another and that reads the same??

I also swapped the CH and HW over over and HW is still fine/no problems at all?

Also looking on page 29 the as temp increases then so does resistance.
So they must be PTC thermistors.

Surely they should be NTC on CH or HW.

My reading of 1.2k when cold/removed at room temp show 1.2k on the new ones I purchased??

So this gives me approx as below (I just averaged the temps for missing specs.

10c. -890
25c. -1000

37c. -1100. Approx
48c. -1200. Approx

60c. -1300

70c. -1400. Approx

80c. -1490
IMG_1464.jpeg


IMG_1463.jpeg

I’m at a total loss now tbh.

Cheers
 
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It’s been bullet proof.
Only had replace fan and PRV since 1997.
No diverter valve as seperate heat exchangers.

I’ve also had absolutely awful model Ferroli like the Domicondens with the clips/rubber seals. Dreadful boilers. !

Any ideas what is going on with the thermistors?
And why it’s tripping on heat exchange over temp ??

Cheers
 
PTC thermistors were not unusual for boilers developed in the 90s when boiler control was less advanced.
Some models had PTCs that had resistances down to a few ohms.
What's the pump like?
 
bilabonic said:
Hi all

My trusty Ferroli 701CH is switching on /off.

I checked the LED status and done a few basic with my multimeter checks and it’s tripping on the CH limit stat/over temp on heat exchanger.

Would the CH flow temp cause this as it’s not adjusting/modulating the gas valve?
I have tested it’s resistance and it seems ok and within range??

Is the gas valve adjustable or just on/off as I suspect?

Cheers
Click to expand...
What are the leds indicating during heating cycle?
 
bilabonic said:
The thermostat on the boiler to set the CH is also ok.
But even when I have it set at at its lowest in order to call for CH the outlet pipe is gets absolutely red hot.
I can not keep my hand on it!

It’s the internal ‘heat exchange limit thermostat’ (50 on diagram) that is switching the boiler even at its lowest setting.

Any ideas?

Thanks
Click to expand...
Check the pump
 
Gasguru said:
PTC thermistors were not unusual for boilers developed in the 90s when boiler control was less advanced.
Some models had PTCs that had resistances down to a few ohms.
What's the pump like?
Click to expand...
Exactly. Only seen them on flues.
 
Pump has 240v going to it.
I have not tested it tbh as my rads weee getting warm after continuously cycling on/off.

It nods no think to check it as I’ve only had pumps fail when they blow a fuse or get red hot with heating off.

What’s the best test. I can ‘feel’ it running. It has 240v on it. But it gets red hot after it’s been cycling on/off.

I’m presuming it was just residual heat after constantly cycling on the 100c overtemp stat??

Plus it’s engaging the flow switch……..

Cheers
 
bilabonic said:
Plus it’s engaging the flow switch…
Click to expand...
What flow switch. Pump run is not checked

240 on terminal means power going to it but it could be slow running so will not blow a fuse but temperature will spike.

You need to look at the led strip to establish what is calling or shutting the burner
 
Ahh. I quickly jumped to conclusions that the ‘Flowmater’ (136) was on the CH. It’s clearly on the HW!!
What a stupid mistake.

All LEDs seem to be fine even though the diagnostic capabilities of them is very vague imo……

Everything works.
All conditions met.
I have HW and CH (trips after hitting limit)
It’s not tripping the

It’s just tripping out on CH Limit stat/Heat Exchanger Limit stat (50).

There is 230v going to pump and my rads are warming up so it must be ‘running’.
After CH is constantly cycling on/off the pump is red hot.
I did bleed the pump and as well but no difference (water was very black as expected).
 

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Ahh. I quickly jumped to conclusions that the ‘Flowmater’ (136) was on the CH. It’s clearly on the HW!!
What a stupid mistake.

All LEDs seem to be fine even though the diagnostic capabilities of them is very vague imo……
LED is the one that is ON/OFF.
Unplug thermistor goes off/adjust HW switches it/overheats it’s goes off as expected.
It’s even telling me the thermistor is ok as it I set it to min and it trips out I have to slightly increase temp for it to illuminate again.


Everything works.
All conditions met.
I have HW and CH (trips after hitting limit)
It’s not tripping the

It’s just tripping out on CH Limit stat/Heat Exchanger Limit stat (50).

There is 230v going to pump and my rads are warming up so it must be ‘running’.
After CH is constantly cycling on/off the pump is red hot.
I did bleed the pump and as well but no difference (water was very black as expected).

I’m thinking it can only be the pump now…

Thanks pal
 
Also what has confused me is that the HW and CH will not work if the new stats I had.
It’s as if the resistance is to to high even though that’s what it requires.
The resistance does not match what I posted above given by on the manual.
The new ones will not work on either HW or CH.
but both my existing work fine. Plus I have have swapped my existing over from HW to CH and it fires as last post.
They should be high resistance.
Anything below 0.5k and led 4 woukd drop out.
 
bilabonic said:
Anything below 0.5k and led 4 woukd drop out.
Click to expand...
Hurray. Finally reached the finishing line.

There are two LEDs, one for heating and other for hot water. Led will drop out like you have found when overshoot occurs.

Have you checked the resistance of the working sensor against what is not working.

Bear in mind, visually these might look identical but operation will be polar opposite

Sensors that are not working should read about 1000 ohms at room temperature, if 10,000 then you have the wrong sensor
 
Last edited:
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