Saunier Duval warm hot water, hot rads

Sponsored Links
no thats the main heat exchanger. wrong one

look at 20.34 page 55.
Hi Mick

Carried out the work yesterday. Removed the plate heat exchanger. Had a look, there were little black specs of dirt falling out when i flushed it through with a hose. Not loads but a small amount.

The two holes at the top, when looking thrugh them, it looked black. The bottom two holes looks clear.

I descaled it twice using Oust descaler. Fitted it, and now getting hot water! Brilliant!

One one minor problem though, i left the hot tap running and had a look at the flames on the boiler and noticed that the flame would start up, go high for about 3-5 seconds, then low for 3-5 sec, then off for 3-5 seconds. Then it would fire up again in the same sequence. I checked the hot water at the tap and noticed it went from warm, to hot, to very hot, then hot, then warm, and this cycle repeated itself.

Personally I can live with this, however I dont think its supposed to do that is it? Any idea what could be causing that?

Many thanks for the help so far! My wife now thinks i'm the bee's knees as she was constantly pestering about the lack of hot water!! Got a big roast last nght for my hard work lol
I suspect the plate still contains a considerable blockage.

But if you are now happy with the hot water you can leave it until more dirt gets into it from the system.

Your system should ideally be flushed or have a magnetic filter fitted.

Sponsored Links
I descaled it twice and flushed it out for a while using mains pressure. The water did seem to flow pretty well, althought the botton half (inside) of the heat exchanger was still black after the deslcaing, with only few silver shiny bits appearing.

So you think it may still be blocked?

Is their any specialist powerful descacler that plumbers would use for something like this?
Can you tell me what chemicals you used to "descale" it?


anyone know if using oust to descale the heat exchanger will damage it?

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links