DHW Problem on a Saunier Duval SD30e

16 Dec 2013
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United Kingdom
Hi All,
I have a Saunier Duval SD30e combi boiler that's giving a little trouble with the DHW.
When drawing hot water, with the tap fully open, the temp only gets hand hot.
It gets a little warmer on reduced flow but will go cooler to cold when the tap is opened to full again then back to hand hot.
What I mean by hand hot is, you can leave your hand there all day without it getting too hot.
When the the central heating is selected and up-to temp, the hot water is OK and hot enough to wash greasy dishes or have a nice hot shower etc.
The boiler is now over 12 years old and the only previous problem was with the DHW flow diaphragm holed and not switching.
I replaced that approx 12mnths ago and all has been OK til now. Any advise on what to check would be appreciated.
Thermistor, diverter, anything else?

Thanks Brian
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Open the hot tap fully and gas rate the boiler...see the FAQs. A common fault is for the PCB to fail to drive the gas valve to the maximum gas burner pressure. However you can't change the PCB yourself as it requires the gas pressure to be confined, so a boiler repair eng. Is required.
Gasguru, thanks for the reply. I have had a gander at the circuit board on the off chance and found some components with typical burnout/ scorch marks.
Looks like your correct and It will need a new board!!!!!
The below img shows the components in question.
Don't know if its worth repairing seeing a new board is £160ish plus fitting etc? Sods law says it will pack in all together very soon.
I will bumble along with it until the new year and then consider changing the boiler, considering its age and the price of gas. Had my moneys worth from it, not cost a penny in the 12 years except for the flow diaphragm.
Now is it Intergas or Atag?????


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Hi, i have a gloworm compact 80E, basically a rebadged SD30e. I had exactly the same problem as you. Burnt PCB, low gas pressure, slowing the water flow to get hot water. The fault was on the PCB. If you look at the PCB, the area to the right hand side of the transformer is discoloured, where components have got warm over time. There is an electrolytic capacitor which dries out, C105. I changed this and got another 2 years out of the PCB before the transformer TR100 then failed.

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