Vaillant Ecomax - Cuts out but no fault code?

17 Nov 2004
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United Kingdom
My parents have a Vaillant Ecomax condensing combi-boiler.
It is at least 4 years old.
It has recently developed a fault I would like some help on.

The central heating works fine, but when hot water is called for the boiler stops working. The display shows no fault code, only the temp as usual, but is flashing. The only way to get the boiler to reset is to switch it off at the power supply for 2 or 3 minutes then it turn back on again.

Has anybody got any ideas as to what is causing this problem?

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An engineer has been out and reckons the heat exchanger is furred up with limescale.
Does this seem like a reasonable cause?
The engineer does not seem very good at diagnosing faults.

Are you really saying that the display flashes the temperature?

There is no fault code?

Never seen the display flash the temp on these :confused:

Are you saying that the hot taps go hot/cold/hot/cold at about 30 sec intervals?

If so the plate will be blocked on the system side most likely.
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Could be sensor or diverter problem. Burner fires up but the heat does not get dissipated.
Any previous history on the boiler?
if it is having circulating problems its not usually the heat ex its normally the rubber hose
Hi Folks,

The boiler was in the house when my folks moved in 3 years ago and has always been ok.

At the moment the central heating works fine, but when the hot water is called for via a tap or the shower, the boiler stops firing (heating).
The display has no error code, but looks the same as normal with temp showing etc, but it is flashing on & off.

Pressing the reset does nothing...the only way to get the boiler to start again is to turn it off completely, wait a few minutes then turn it back on.
The heating will kick in again, but calling for hot water stops it again.
The engineer fitted a new heat exchanger today.....the fault returned this evening.

Any tips as to what I should be checking for anybody?
I'm hoping to visit the folks this weekend and would like to have a few clues as to what I should be checking first.

My old man was going to be on the blower to him first thing this morning, make no mistake.

The heating has now packed in too! Apparently he was back this morning and diagnosed "**** in the system". He has gone off to get a divertor valve as that is now blocked. When he returns he plans to flush the system and fit new valve. Apparently he will be adding a chemical to the system that will break down all the debris, and return after Christmas to flush the system again and then add inhibitor.

We'll see if he gets the boiler working again old man is not happy :eek:
Assuming he left the old heat exchanger on site, your father should be able to easily ascertain whether he has a dirt problem or not.

Never seen a flashing ecoMAX display before either.

You could ask your old man to start it up and press the i button. This will tell him where the process stops if he references the S (status) codes in the manual.

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