Ferroli Optima 901 -occasional Hot water problem?

22 Feb 2006
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United Kingdom
Ferroli Optima 901 -occasional Hot water problem?

Hi I have a Ferroli Optima 901 combi boiler and have recently been experiencing occasional problems with no hot water.
This has been noticed when running the bath, with it initially running warm and then running freezing cold.

I think I may have loft gremlins as when i get the step ladders out to access the loft, go into the loft, look at the boiler to check the pilot light and system pressure and then try the hot water again it seems to of rectified its self!!

I have in the past (6 mths ago) had problems with the ch side loosing pressure which was resolved with replacing the PRV.
The pressure in the boiler was repressurised to 1.5 bar (while cold). and rises to about 2.25bar when the CH is on, i assume that this is correct due to the expansion caused by the increased temperature.

The only thing I can think of is that the problem seems to happen when the CH is not on (or at least thats when ive noticed it) thus the CH system pressure is at its lowest. I know the Boiler shuts down at 0.5 bar, is it possible for this sensor/valve (or whatever) to be faulty? Or any other ideas?

Is it possible that it is the air pressure switch or is that purely there to monitor the operation of the fan?

Sorry for the ignorance, trying to understand whats going on and hopefully fix it - if it is an issue thats caused by the heating being off!

Thanks Chris
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Hi thanks for the quick reply. Any advice on how to carry this out would be greatly appreciated. I have the main cover off at present along with the bottom cover.

Dont spend much time repairing boilers but i think the optima has a paddle switch on the incoming main that fire's the boiler.if thats the case these sometimes just need cleaning out, Brass fiiting with 15mm unions on each side & a lead running off the top.need isolate cold water before removing. found under bottom front of boiler.
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Hi thanks for the advice, any more advice on what the paddle switch looks like and roughly where I can find it. It appears to occur more when I am running the bath, ie attempting to heat up a larger quantity of water. If i then stop running the bath and turn on the basin hot tap the water will eventually run hot!!
Thanks all for your assistance
It's the blue bit.

Sounds more like heat exchanger problem, but Ferroli's two temperature sensors are renowned for causing problems. If you haven't got the kit to check the temp drop across the heat exchanger to diagnose, changing the sensors might be worth trying.

Are you in a very hard water area?
Hi Chris thanks for the diagram that helps a lot. Which numbers are the two temperature sensors you refer to, it may be worth changing them just to elminate those from the equation.
Nope not in a hard water area.

Thanks Chris
Cheers Chris, I'll order these sensors and replace them (just in case) and then isolate the cold water and clean out the paddle switch, see if that has any effect. thanks a lot for your help.

Hi there, So I have now replaced the Flow (paddle) Switch on the HW side and also replaced the two temperature sensors for the HW and CH.

I thought I had cured the problem, but then I ran the bath last night and half way through it ran cold!!!
I turned the tap off and tried the tap on the basin in the hope that a smaller flow of water may bring the boiler back to life but nothing.

I then put the CH on and waited a couple of minutes before turning the hot tap on and bingo... Hot Water. Now I dont know if its a coincidence or not. Any ideas which direction i should be going in?
i had one that was doing the same and i swapped the thermistors (NTC) and all was well. they come as a pair so make sure you swap both CH and DHW NTCs.
Hi, thanks for the reply, I presume you mean items 34 and 42 in the diagram in the thread above. If so these are the temp sensors I have just changed along with the flow sensor :(
Any one else got any other ideas

chrisstorey1 said:
Hi, thanks for the reply, I presume you mean items 34 and 42 in the diagram in the thread above. If so these are the temp sensors I have just changed along with the flow sensor :(
Any one else got any other ideas

yeah sorry i missed read the above post. at this point id be ringing ferrolli technical. They will only speak to you if you are corgi reg tho im afraid.
It could be that the very first answer was right. Boiler can't get energy into the HW fast enough so it overheats and cuts out. Blast of cold water from the CH cools it. Can be checked with surface temperature probes to see if that's it.
Or it could be that the gas valve isn't turning itself down (modulating)properly. Corgi job to check and adjust.
Thanks for the help guys, How easy is is to clean the heat exchanger? Is it a matter of removing the panel on the front under the main casing?

Or does it sound like I need to get a proffessional in! Just a bit reluctant after getting stung last time just to change a PRV. I know I should of changed it myself but I didnt know any better then. :confused:


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