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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 3629
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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I have a problem with my Ferroli 31HC Optimax boiler - a d2

Customer Question

I have a problem with my Ferroli 31HC Optimax boiler - a d2 code appears when the central heating is on. It doesn't appear all the time, but typically now when I really need it - it's showing. The hot water is fine, although a d1 does appear after I turn off the taps.
The d2 will appear when the temp on the heating of the boiler goes up through the 60's-70's upto the 90c, and will shut down temporarily. It will then fire up again, and constantly repeat the above. This mean that only one radiator gets hot, some others are warm and others are cold.
Sometimes (when d2 doesn't appear and all works well) the temp on the boiler for the heating remains at about 30-40-50 deg C.
Any advice? We have a 16 month old son so getting desparate.
The plumber is waiting for a part, as the boiler's been moved and we now use a vertical flue rather than a horiztonal one, and he thinks he needs something else now.
Submitted: 5 years ago.
Category: UK Plumbing
Expert:  Andrew Smith replied 5 years ago.
Hi my name is Andrew - lets see if we can get you sorted in the shortest possible time. The boiler is overheating. What is the system pressure and is the pump making any strange noises?
Customer: replied 5 years ago.
The pressure is around 1 at the moment. I've had the d2 code in the past and have increased the pressure to around 1.5 , however the boiler started leaking then, so I reduced the pressure again by opening a radiator and releasing some water.
I wouldn't say it's doing a funny noise as such, it does sound as if a fan or something is working even after the heating has switched itself off (this was before the d2 code).
Expert:  Andrew Smith replied 5 years ago.
Could it be the pump? Right hand side at the bottom?
Customer: replied 5 years ago.
I don't know. Is that what you think?! Wouldn't that mean no hot water being produced either though?
Expert:  Andrew Smith replied 5 years ago.
If it is airlocked or not fully working, you may get partial flow. Can you take the cover off and see where the noise is coming from?
Customer: replied 5 years ago.
At the moment there isn't any undue noise. I had switched the boiler off for a few hours and now when I switched it back on the d2 message doesn't appear and it works well. However, this was also the case yesterday eve but it stopped working during the night and the d2 code was there this morning when I checked. If it was the pump would it be constant fault rather than this seemingly intermittent one? So no noise coming from pump now.
Expert:  Andrew Smith replied 5 years ago.
It could be air in the pump - Can you take the cover off and vent the pump with a screwdriver?
Customer: replied 5 years ago.
Sorry, and this might seem a stupid question - but how do you "vent the pump with a screwdriver"?
What do I do?!
Expert:  Andrew Smith replied 5 years ago.
The big screw in the centre. Undo it slightly and see if you get any air out of it.
Customer: replied 5 years ago.

Hi Andrew,


There doesn't seem to be any significant noise coming from the pump, and the fault seems to be intermittent.

The heating and hot water had been working fine tuesday to saturday - but the problem re-emerged sat afternoon -i.e. radiators not getting very hot and d2 code appearing. I had inadvertently switched off the power to the boiler in the morning.

Putting the boiler on standby for a few hours seems to rectify the problem.

On sunday eve, the heating was working fine, but couldn't get any hot water.

By this morning (monday), the d2 appeared again - most rads cold, but hot water worked again.

So the situation is not resolved, unfortunately.

Expert:  Andrew Smith replied 5 years ago.
This is a strange one, the boiler will overheat (d2) but the water will still work?
Customer: replied 5 years ago.
Hi yes. Even when the heating is playing up - d2 code keeps appearing every couple of minutes, we can still get hot water from the boiler.
Expert:  Andrew Smith replied 5 years ago.
OK, I think the first thing to do would be change the return temperature sensor thermostat to rule that out. Try your local Parts Center or PTS for the part.
Customer: replied 5 years ago.
Hi thanks for your help. I needed to call a plumber out in the end and he changed the diverter valve as it was sticking and seemed to have corroded a bit. So thanks for your tips, but unfortunately your help didn't resolve the situation and so I'm not 100% satisfied and don't think I should Accept your answer, and so don't authorise the payment. Thanks.
Expert:  Andrew Smith replied 5 years ago.
No problem, but it is hard from this far away going from the answers you have given.
Customer: replied 5 years ago.
Yes I accept that. Thanks for trying all the same. Merry Christmas.

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