Central heating temperature on Ferroli Optima 701 boiler

14 Feb 2015
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United Kingdom
Hi there.

I have just moved into a property that has a Ferroli Optima 701 boiler. I am not sure whether there is something not right with the central heating hot water supply from the boiler.

The DHW is red hot, almost scalding. I cannot hold my hand on the outflow pipe on the DHW.

The CH outflow pipe is warmish and the radiators never get what I call that hot. While the CH is being demanded, the main burner is lit constantly and is not going on and off.

The DHW is fed by a 15mm pipe and the CH is fed by a 22mm pipe

Could it be the larger pipe size and hence a faster flow rate that is causing the CH not to get hot ?

Any advice would be greatly appreciated.


Chris Brennan
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Sounds like your diverter valve is stuck, turn the hot tap on and hold your hand on the flow pipe 22mm, if this gets hot its your diverter.
Easyflow, go easy with flow of knowledge here :D

Boiler does not haves a diverter valve!

The hot water, initial run off WILL BE scalding as it has been sitting in the heat exchanger until hot tap is run Once you have used up this 'stationary' water, temperature should stabilise unless your flow rate is minuscule

Boiler, if it is 24kW, will heat 9.5l of water through 35 degrees if it is in good nick and has correct amount of gas available to it. So, you will notice if incoming water is 5 degree C cold, hot tap will be at 40 degrees.

If you are running the boiler at 70 degree C for central heating, initial slug of water will be at 70 or thereabout to then drop to 40 if aforementioned scenario exists.
Correct DP, Naturally thought it was another Ferroili problem :oops:
  • Thanks
Reactions: DP
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Thanks guys for your input on this.

Regarding the slug of water first out of the heat exchanger, I can understand that, but even when having a shower, the water is still coming out red hot from the DHW part of the boiler.

There is definitely not a 35 degree temperature differential between the infeed and the outfeed on the CH pipes when there is no DHW demand.

Some more information : When DHW is being drawn while the CH is on, and then the DHW is stopped, the boiler does not kick in again for the CH for a couple of minutes. This is almost like a divert valve changing over, although you mention that there is no divert valve on this boiler. Not sure if this is normal or not ?

If you have any more comments on this, I would be interested to hear from you.

Thanks !

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