Vaillant Ecomax 835/2E

[Ron]

We have a Vaillant Ecomax 835/2E, which was recommended and fitted in

2003 by our neighbour who runs his own gas fitting business and who does our servicing of it. Recently the boiler developed a problem with hot water delivery. The water ran very hot for about 30 seconds then slowly cooled over the next 2 minutes until luke warm. We found that by turning the tap on very low, thereby reducing the flow of water it was possible to run a bath in about 20 minutes. We asked our gas fitter neighbour to carry out a repair for us. He replaced the diverter valve and NTC sensor. Removed the heat exchanger and flushed it through with a machine and a cleaning solution. We also decided that it would not hurt to add a Magnaclean appliance to the system to help remove the accumulation of black sludge that forms there. This was fitted and a bottle of SM3 system cleaner was added and ran for 2 weeks before flushing and refilling. All of this has made no difference and we still have the exact same problem. Our fitter phoned Vaillant several times for technical advice and they advised changing the heat exchanger but because the actual flow of water is very good with the tap full on the heat exchanger does not appear to be blocked. We are now in an embarrassing situation with our neighbour and friend, in that we have spent a fair amount of money on a repair that has, so far, been unsuccessful and are scared to replace the heat exchanger, when it seems by no means certain that it will solve the problem.

With the hot water thermostat set at half way and the tap full on Boiler reads 71 C after 25 seconds Then starts to drop 47 C after next 30 seconds 39 C after next 30 seconds 35 C after next 30 seconds 34 C after next 30 seconds Remaining at 34 C thereafter.

I would be most grateful for any advice you may be able to give.

[YAPH]

Are you in a hard water area? If so, what sort of scale inhibitor does the system require (see the installation manual) and what type does it have?

[geoff]

In message , Ron writes

filling

I would rarely point people to the diynot forum, as it's populated by a load of sad fitters with no life

in this case, I think that you might find someone there who might have an answer

don't forget to point out that a CORGI fitter is doing the work, they can be a bit sensitive

[Stuart Noble]

This is why I prefer the insurance option. They can replace things on a trial and error basis at their expense rather than mine.

[dennis]

As all of what you have done appears to be for the primary heating side I am not surprised it had no effect on the hot water.

Is this the problem? Is the flow of water too high? Combis usually have some sort of flow limiter to ensure that there isn't too much water going through them. If there is they can't heat it fast enough. Is the flow faster than it used to be? Does it start of slow (and hot) and then increase (and cool)? Has anyone checked the flow limiter is still working?

Time how long it takes to output 5-10 liters and post the results here and someone can work out if it is just too much.

I would do a few flow checks first.

[Ron]

Thanks for the input.

We are in a hard water area SE London. The water goes through a water softener (Permutit Ecowater) So I would hope that would deal with water hardness. I ran 10litres of hot water with the tap full on from a standard kitchen tap in 56 seconds. If the tap is only turned on a little, as the water starts to heat it will slow to about half the rate or even stop. I think this could be some sort of safety thing. If I turn the tap on 'just enough' it will run hot all the time but will take 20 minutes to run a bath.

[Ed Sirett]

What is the actual flow rate of water you are getting out of the hot tap? What speed is the combustion fan working at during HW production this is on parameter d.33 or d.34 (if they are different to each other then that is also significant).

The NTC would be the obvious thing to change but that's been done. What effect does moving the max HW temp dial when doing HW?

[David]

I have a diynot account, I can post this on behalf of the OP if he wishes.

There are a few Vaillant approved engineers on there apparently

[geoff]

could do, but, there's nothing to stop him signing up

... fitters - please

they don't and are not allowed to, engineer anything