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Plumberpro, Mechanical Engineer
Category: HVAC
Satisfied Customers: 634
Experience:  Over 20 years experience in plumbing heating and gas
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hope you can shed a little light upon a frustrating problem.

Resolved Question:

hope you can shed a little light upon a frustrating problem. That being a ferroli optimax 38 hec plus, hot water starts out fine and then starts to fluctuate in temperature, have checked:- changed dhw & heating thermistors, changed plate heat exchanger all good.
The central heating works OK
Checked water flow rates between hot and cold systems they are identical
In central heating mode the gas valve seems to be modulating OK as it regulates heating according to heating return temperature, can you advise please as to what the likely cause is?
Thanks time
Submitted: 2 years ago.
Category: HVAC
Expert:  Andrew Smith replied 2 years ago.
***** ***** : Is this just affecting the hot water?
***** ***** : Can you check that when you lose heat to the water you put your hands on the central heating pipes under the boiler and see if they are getting warmer?

C/H is OK there is no flow to heating when in DHW mode nor is there backflow down return on heating system the temperature indicated by the control panel varies up and down 35-47c, but on using temperature sensor (infrared remote) on the pipework the readings are incorrect and do not relate to control panel


having problems getting through to you hope my additional information reached you, please "E" mail your answer to question, thanks, Paul

Expert:  Plumberpro replied 2 years ago.
, do you still require help? Do you have any fault codes come up?
Customer: replied 2 years ago.

no fault codes on control panel, the fault affects dhw only and not heating which functions OK, in heating mode the firing rate of the boiler seems to regulate up and down as would be expected. The plate heat exchanger is OK as are the dhw & heating return thermistors ( renewed) dhw and cold water flow rates are identical as are the pressures.

I surmise that as there is no affect on the heating flow and return pipes when dhw is drawn, the diverter valve is functioning as per design.The only other thing is the flow meter,the filter is clear, could that partially fail? Thus causing the fluctuating dhw temp

Expert:  Plumberpro replied 2 years ago.
Yes , the flow meter is the only thing it could be ,unless you got a faulty part. You have replaced the thermistors , board and heat exchanger, so literally the onlyvbpartvleft on the hot water route is the flow Meter.
Plumberpro, Mechanical Engineer
Category: HVAC
Satisfied Customers: 634
Experience: Over 20 years experience in plumbing heating and gas
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