Ferroli Falcon Hot Water Problem

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A few weeks ago started getting problems with DHW on this 9 year old Ferroli Falcon. I realise it's old for a boiler but could really do without replacing it unless repair becomes much too expensive.

Problem is this.

Start running bath. Runs hot. After a few minutes, maybe 10 the boiler cuts out. However the DHW demand light is still on.
If you turnoff the tap and then try and run again, runs cold. turn of boiler and cut power Wait 10 -15 mins try again will normally run a bath full of hot water no problem.

So read forums and suspected heat exchanger full of scale.

Had Powerflush come in on Friday and flush the hot water part of the boiler with descaling chemicals for a couple of hours. (£300) So presumably it's now fully descaled. Thought all was well as run DHW for 15 mins no problem. However next day exactly the same hot water problem returned.

Should i now be looking at changing the DHW temp sensor? Assume diverter working ok since demand light stays on.

CH is normally fine though i have noticed that occasionally it will cut out in the same way and re light and cut out again. But mostly the radiators are hot when they should be.

Any advice gratefully received.
 
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it sounds like a thermistor playing up, try changing both the ch and dhw, they are cheap enough if thats not the problem at least it elimanates them, cant remember but they may be clip on.
 
it sounds like a thermistor playing up, try changing both the ch and dhw, they are cheap enough if thats not the problem at least it elimanates them, cant remember but they may be clip on.

Thanks for your very prompt advice Picasso. Just to check by "Thermistor" you are not referring to the DHW flow temp sensor which screws into a pipe in the lower part of the boiler, but either the safety overheat thermostat or the central heating flow limit thermostat both of which clip onto pipes on either side of the heat exchanger?

Thanks again Picasso :)
 
just had a look , both the thermistors are wet pocket so the boiler needs to be drained down if you want to change the ch sensor, the dhw is on the hot water outlet (to the left of the gas valve) and the central heating one is under the low pressure switch,

It will be easier to just replace the dhw sensor as you dont have to drain down the boiler.its just a matter of turning off the cold water supply.
 
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Thanks again for checking that out for me.
So I'll get a dhw flow temp sensor tomorrow, fit that and let you know.
I had to chance the ch flow temp sensor last year so i guess it makes sense that it's partner has now also failed,

You are a very kind and knowledgable man.
What a powerful combination! :LOL:
 
Replaced DHW flow temp Sensor. Very easy to change as Picasso stated.
Seems to have worked like a charm. Guess I could have saved £300 on getting the boiler descaled. Though it's probably as well i had it done after 9 years in london.

Thanks again to Picasso, You're a star!
 
Ran a full bath no prob. Left for an hour. Went to add more water and guess what. DHW demand light on; no firing up of boiler. I'm now wondering if it could be either the safety overheat thermostat or the central heating flow limit thermostat both of which clip onto pipes on either side of the heat exchanger (With a sort of white paste between the part and the pipe) inside the sealed compartment.
Heating still seems ok.

Any ideas?
 
sorry, I would have to be in front of it to go any further.
 
Appreciate what your saying. Assuming if you are a pro in Essex that SE London would be out of your normal area of working? Thanks for all stirling assistance.
 
It might be possible that the Air pressure switch is dropping out although I am unfamiliar with the control panel I am not sure if this would flag a fault?
If the domestic hot water light is still on then of course that means the boiler is still thinking its doing hot water.
As far as I was aware both termistors are supposed to be changed at the same time on this boiler.
You may presume that the C/H thermistor is not in operation when a tap is running but on many boilers it is used as a control for primary flow temperature. Even though you changed it last year again its a cheap try.

Regards Stan
 
Thanks very much for your input Stan. That is interesting, and your right I did assume that the CH thermistor was uninvolved in DHW production.
I will change the CH therm as well. Hopefully tomorrow.

I just noticed however that the boiler is sometimes cutting out when doing heating. Was just in the kitchen and heard it cut in for heat for about a minute then out then immediately re light and on for about 30 secs then cut out. However the heating is generally very hot but thought it might point the way to know that this was occurring. FYI the boiler does not have a room thermostat, temp is controlled on the boiler.

Could it be a problem with either the safety overheat thermostat, or the central heating flow limit thermostat? Both of which clip onto pipes on either side of the heat exchanger? Or is it more likely to be what you suggest the air pressure switch going faulty?

Thanks again!
 
id be thinking that the venturi is failing not an expensive part but an rgi is needed to change the part as its in the combustion chamber. it will be doing it on the central heating too but you will not notice it as much. who suggested the flush off the heat exchanger?

Nath
 
Is the Venturi part of the fan assembly? Asking as this has recently been replaced? As far as de-scaling the HE goes, it seemed to be the consensus that after 9 years of hard water the HE may be clogged with scale and this would reduce flow and cause an overheat.

Since this boiler is much the same as the Modena searched for that and found someone with the exact same symptoms who said:

"After several years, I finally bottomed the problem on my Modena 80, which kept shutting down when running DHW.
The overheat stat on the upper left hand side of the heat exchanger was operating at around 50 deg, instead of 100. It's actually a mechanical device operated by a bi-metal pad - The excess force of the spring clip used to mount it pushed in the face plate in slightly, causing it to switch off at a much lower temperature than it should. "

Certainly sounds plausible?
 
certainly changed several overheat stats on the modena 102

the brown venturi with the self tapper screw is best for the falcon if it is the red one changed plenty of these.

just there is on thing which i hope it isnt is the board as if the boiler isnt modulating down it could be one off the resisitor take the pcb cover off n check the resistors dont have any discolouration round them.

Nath
 

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