Ferroli Modena 102 - Fault find for me please chaps!!

[Dannypipe]

Hi all, I've been out to repair a Ferroli Modena 102.

The hotwater is running hot, then the burner shuts off and the water turns cold. Then it sparks up again and turns warm again.

Also the heating cycles (it turns on, burns and then cuts out, then within seconds sparks up again and runs, so on).

This could be because the boiler is far too big for the little house its in. 6 rads in total.

I have fitted a part suggested to me by the fault flow chart, which I didnt agree with 100% so I called Ferroli and they agreed with the chart. (Water Pressure switch) - It didn't work, but then I forsaw this.

I need to get it done on my second visit as I'm so pushed for time, plus my other half now fully 9 months pregnant, so any day I'll have to drop everything and help her out!

Figured Gas Man would have experienced something along these lines. I have my suspicions that either a thermistor needs changing or the DHW sensor needs changing.

Oh and the client said that since I changed the Water Pressure switch, the ignition is much quieter....I said it shouldn't be. My thoughts are that when i drained the boiler to fit the part, I may have removed some S*** from it as the water was as black as coal.

Thanks in advance for any responses. Sorry to have banged on!

Danny

 

[cjg]

flame detec fault?

 

[Dannypipe]

Possibly, I would doubt it would run as well as it does though. The house is piping hot, there's no complaints from the client about the central heating side. Though as I said, I noticed it clicks on and off reguarly. I've not run the boiler from a cold system which would be interesting to do as I would then be able to tell if it was the flame detec, as it would still cycle like it does on warm up.

If it heated consistently from a cold system until it reached temp, then i would be able to eliminate flame rec.

I have suspicions that the reason it cycles on heating is that the boiler is so oversized but that could be a red herring.

Thanks for reply.

 

[Blake]

There are several things that could cause this mate, thermistors, poor circulations, APS etc etc.

Have you checked the thermistors for correct resistance?

 

[Billy Bob Bob]

right danny pipe first suspect is the thermistors,but have you removed the combustion door and tried it?if it runs normal its a good chance the plastic venturies have collapsed but be warned as soon as you remove the hoses they will break anyway,if not venturies then aps also check gas pressures

 

[Blake]

Also has the boiler always cycled on heating, if it was an issue with being oversized I would have expected it to have always done it.

 

[hihowudoin]

maybe DHW waterways in Heat exchanger scaled up causing OH ?

 

[Billy Bob Bob]

my moneys on the venturies or thermistor

 

[stevetheplumber]

i see very few scaled heat exchangers its usualy dirt in the heating ways of the heat exchanger id make this the first thing i looked at drop the plate heat exchanger and see how much black crap is in it
its usually two screws to get this of
as boiler runs fine on heating it has to be something that only functions on hw

 

[Billy Bob Bob]

it does not have a plate heat steve

 

[hihowudoin]

beat me to it gasman lol, dual flow heat exchanger on this model

 

[Billy Bob Bob]

yes its a twinpass,most ferrolis are except that new band a shed

 

[Dannypipe]

Cheers guys, brilliant advise as per.

I don't know if it has always cycled during central heating only as client was unaware, though they did say the hotwater was consistent.

I haven't checked the thermistors for correct resistance as I can't get the figures i need, the tech Ferroli guy was even vague!

I haven't removed the combustion door as yet, thought I'd post a thread on here first so i can check the right things on the first pass and save time on site.

I suspected a thermistor, but didn't really think about the venturies.

Good advise lads, I will open the door tommorow and check the venturies, the impulse hoses...don't think I have the figures to check the aps.

I will photograph whatever the culrpit was and post back here tommorow evening. Thanks everyone.

 

[Billy Bob Bob]

be carefull with the hoses danny,i would advise you pick up a set of venturies at £6-9 they are not dear,you are in trouble if they fall apart,unless your skilled with the old super glue LOL good luck mate let us know how you get on with thermistors you get roughly 11k when cold,resistance reduces with temp

 

[Dannypipe]

Cheers for the heads up. I will report back with lovely piccies tomorrow evening!

I'll swing in to PTS in the morning and pick up some venturies, I'm not handy with the super glue, tend to stick my hands together most of the time!

 

[Billy Bob Bob]

LOL fan comes out easy to replace them if needed

 

[mikegas]

its prop basic but why does the boiler fire with the cover off if the venturi has fried?

 

[Billy Bob Bob]

what tends to happen is the venturie snaps and moves in a sealed combustion chamber the boiler plays up,take the door off you introduce a extra welter of air aps then makes and the fault goes,you can also use this method on a aps with a failing diaprahm

 

[mikegas]

so your just introducing more air to help create a greater + an - pressure, so if the venturi had melted and completely blocked removing the cover wouldnt help?

 

[Billy Bob Bob]

so your just introducing more air to help create a greater + an - pressure, so if the venturi had melted and completely blocked removing the cover wouldnt help?

no,but if a bit had broken off,or in the modenas case broken and moved yes