Difference between revisions of "Vaillant Ecotec plus 624 repair"

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Revision as of 22:53, 31 July 2019


This is a quick overview of the procedure I followed to replace a leaking main Heat eXchanger (HX) in a Vaillant Ecotec plus 624 system boiler. (the procedure would be much the same for many Vaillant boilers made in the last ten years or so.

This is not intended as a primer in boiler repair. It is assumed that you are competent to do this kind of work and have the required skills and tools. If in doubt call a professional! See the Boiler repair article for more guidance.

The problem

Over a period of time the central heating system had been showing slow pressure loss. This had got to the point were a litre or more was being lost per day. This is obviously not good, since it could mean loss of water into the fabric of the house and the possibility of supporting dry or wet rot, or damage to decorations etc. Its also not good for the heating system since one is introducing fresh water all the time, and hence more oxygen, hard water scale, and corrosion.

Hunt the leak

There were no stains on the ceilings downstairs, so it seemed unlikely it was the upstairs radiator piping. Checked thinks like the drain point outside and also the pressure relive blow off pipe for leaks (small plastic bag fixed over the end), again nothing. So then several days spent getting under the downstairs floors, creeping around the crawl space, and ... nothing - it all looked good. So with a bit of thinking, that only left the boiler itself. There was no obvious water near that, however being a modern condensing boiler there is one place it can leak and not be obvious - inside the primary heat exchanger. Any loss there will be directed into the condensate drain. So I turned the boiler off for a couple of hours, and emptied the condensate trap. A bit later the trap was half full again! There was also some discolouration of the plastic f the trap, which is also unusual - normally the water is here is crystal clear.

So we have a culprit, now all we need is some warmer weather!


I found a really good local(ish) company that had the right reconditioned part in stock (it seemed excessive putting a £400 new part in a 7 year old boiler). The were also able to advise on the exact part needed, and quick fixed an omission from the order with no fuss and next day delivery. For the fix you need the HX itself, plus a new main gasket for the burner and the kit of extra bits like the nuts for fixing the burner (you are not able to re-use the existing ones as they have a "one time only" insert to lock them in place). Plus other washers etc as might be required.

VaillantBoilerHXMainSeal.jpg EcoTec+ 624 Empty.jpg EcoTec+ 624 OldHX.jpg BoilerRatingsPlate (Medium).jpg EcoTec+ 624 AirIntakeOff.jpg EcoTec+ 624 HXFuseableLink.jpg EcoTec+ 624 ExpansionChamberConnection.jpg EcoTec+ 624 HXPipeConnections.jpg VaillantBoilerHXModel.jpg