On Tue, 04 Apr 2006 22:16:14 +0000, maxim naumov wrote:

Ed Sirett wrote:

The heat transfer is so restricted by the chalk that the boiler cylces
between minimum and off gas rates.

don't understand. surely this means that the heat is just lost into the
flue and that water temperature in the exchanger would be lower ? I see
something quite different -- the water is quite hot.

OK you may simply not have the required flow rate of DHW. since you
haven't reported back the flow rates. I haven't got a clue.


IME this fault is not common and would be at least as likely to be PCB
driving it as the gas valve itself.

yes, I'd think so. I'll try to check the driving signal.

Typically the modulator is driven with 0-9Vdc.


That's why you need help.

yeah, maybe it is time to call for professional. 8)


the old sensors looked dodgy. the DHW one is fit loosely in it's casing
and I suspect the internal contact may be bad. I bent the pins and
rotated the internal plastic part -- it helped. it does not cycle that
often anymore.

OK.

...on a Ferroli but on most other makes it has a lot to do with it.

to maintain DHW's constant flow ? seems unnecessary for common water
mains supply, where pressure is always quite high.

No on most combis the pump move the primary water between the primary and
secondary heat exchangers. ON a Ferroli there are two primary heat
exchangers.

In neither case does the pump move the DHW which would be unnecessary,
bad for the pump and illegal.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html