Ferroli Modena 80E Lots of Hot Water but only Warm Radiators

27 Apr 2021
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United Kingdom
Hi folks,

Basic set up no timer or external components. No issues whatsoever with hot water which got a new thermistor from me recently due to its having failed. Previous owner had boiler regularly serviced and seems otherwise in good shape.

Switch on boiler at mains for heat, burner runs for 10-15 minutes warming rads then switches off. Radiators are merely warm not hot which leaves the flat cold. I released pressure and changed C/H flow temperature sensor. Pressurized expansion tank to just under 1 Bar, C/H to just over 1 Bar (Tested original sensor and although old appears to be functioning correctly.) No change. Water in system is clear and has inhibiter. Changed speed on pump, it made a noise so replaced pump with exact same brand new pump but no joy, still the same. (Old pump is spinning freely and now a spare.)

Once warm the boiler shuts down for a minute or two, flashes standby then fires for a minute or two and continues to run as such, on off, on off, never getting hot. Bled each rad, no air apparent.

Seems also to be loosing pressure overnight suggesting possible problem with expansion vessel possibly a sticky Schrader core. Any suggestions most welcome.
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Temperature knob spindles working...check the potentiometers on the pcb actually turn.
Isolating valves under the boiler fully open?
Brand new pump or an ebay refurbished pump (from lying traders).
Leak most likely from the safety valve or on the rads/pipework.
How many times do your tyres go flat...schrader valves are reliable and the cap is a secondary seal.
Thanks for your quick reply. Interesting points. The Spindle on the temperature knob was broken by someone? I have removed the remains and yes using a small screwdriver made sure it was turning and set to max. I will replace this part once boiler up and running. I will check the valves after work as you suggest. Pump head was as you say, from Ebay and described as new - who is to say not refurbed if they are lying as not in manufacturer packaging. No apparent leaks at any rads and heating used to be fine before. There is a small weep at expansion tank showing some furring up. I mentioned the Schrader valve for on pressurising the vessel it did stick open on release leaving a hiss and had to do again. I don't recall my tyre valves ever sticking like that.
Pumps can't be refurbed whatever they say.
The schrader on the Modena is at the vessel base AFAIR so more prone to water corrosion.
The Honeywell pcbs in these models are prone to the solder joints breaking but also suffer with strange faults.
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Personally I am not convinced the pump is the issue. I am satisfied both old pump and new were fine and speed was never an issue as it was never changed until looking for a cause.

Some time ago, following the hot water failing I fixed this but at about that time the CH never got hot. Did the circuit board get wet? Not that I was aware and was very careful not to allow.

Is the board to blame? Personally I suspect that is where the problem could be so for £40 plus I think I should consider changing such. My evening changed so never got a chance to examine the isolation valves as per above but the problem arose without altering said valves and only I had access to such to my memory.

What is interesting is that no one seems to know why?

I have no boiler training only 40 years of cutting out the contractor not having the funds to pay him whatever his trade and whenever involving a tradesperson 90% of the time they mess you about.
It's a ferroli they do strange things.

However the description you offer leads itself to be a flow issue.

A flow issue doesn't have to be the pump, it could be a blocked or choked heat exchanger, or a blockage within the system somewhere.

I had a ferroli at my last house and tbh it was alright, had some o ring issues early on but got sorted. Then we had an issue with the boiler cycling and only half the rads getting hot, transpired someone thought it be a good idea to install tap Flexi pipes and these had.broken up inside and restricted the flow substantially That it couldn't work. Replaced them with copper pipe and a filter the boiler then performed rather admirably from then on, was a pleasure to own and reliable for the 5 years I was there.
Thanks for feedback. The heating was ok before. Nothing odd in pipework but will try shutting off rads apart from nearest. If it was heat exchanger would this not also affect the DHW which is ok?
Your boiler has a Bi-Thermal heat exchanger, disconnect the DHW flow meter/switch, just pull the plug off, does the heating now work ?

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