Ecomax 824/2 E NTC fault?

[hairyfingers]

Hi

I have just moved into a house with an Vaillant 824/2 E boiler. Heating seems to work fine DHW was only getting luke warm. I noticed the CH flow pipe was getting hot when DHW was operated so changed to Diverter Valve. this seem to have solved the CH flow pipe problem and now DHW get super hot -

The problem is - is it now getting too hot??. The DHW temp dial seems to make no difference at all to the actual tap temp. When tap is switched on the boiler display heats up and up and up until it reaches 85 degress on the display then the boiler cuts out - the temp display decreases a few degrees then the boiler kicks in again until 85 degrees, cuts out and so on and so on..... (presumably the 85 degree cut out is some kind of safety cut out)

the maximum temp the DHW dial goes to is 64 degrees so I'm guessing it going up to 85 degrees when switched on is not right??

could it be a dodgy NTC monitoring the temp incorrectly. I can see 3 NTC's in various parts of the boiler but I'm tempted to change the one next to the DHW heat exchanger to see if that does anything or do they all work together?

any thoughts?????

 

[petit_pablo]

More likely to be a restricted plate heat exchanger. The heated water cant circulate so it backs up to the main heat exchanger causing the increase in temperature and the cycling you describe.

The temp you are seeing on the display is the primary water temperature, not the domestic water temperature.

 

[picasso]

Check that the spindle hasnt broken off the end of the hot water dial, the symptoms sound more like blocked plate heat exchanger but could be a dodgy ntc although the ntc,s on vaillants are very reliable.

 

[hairyfingers]

Thanks for such speedy responses!

If I take off the secondary heat exchanger and flush it through with mains pressure cold water is that likely to help or is a new exchanger required?

would the symptom of the DHW temp dial not affecting the actual tap temp also correlate to the exchanger being restricted/blocked?

I don't think the spindle is broken as the target temp changes in the display when I turn it.

thanks

 

[petit_pablo]

Do you have a thermometer?
The tap temperature is probably not as hot as you think it is!


With the plate heat exchanger, yes you can flush it through. You would be best to get a bottle of DS40 or similar from a merchants and use some of this in the system side of the plate to remove all the carp. Make sure its throughly flushed with clean water before you refit it.

 

[hairyfingers]

No I haven't actually tested the water temp with a thermometer - could well be worth doing.

But I guess that doesn't change the way the boiler has to activate what i think is a safety cut out at 85 degrees.

I'll take the exchanger off tommorrow, flush it through and report back.

thanks

 

[mickyg]

plate heat exchanger scaled

mick

 

[Beerlover]

Not sure it is a blocked plate heat exchanger, this normally gives poor/fluctuating hot water.

Do you get the same rapid heat rise in the display when central heating is on?

In CH mode the boiler should light in low gas and stay that way for a couple of minutes before going to high gas.

I KNOW THE RULES ABOUT GAS ADVICE

Watch the flame size through the sight glass

I suspect it is a gas valve problem, for which you will need a RGI

 

[hairyfingers]

Haven't had time to take off and flush exchanger today but did switch heating on to observe. The CH seems to work fine - I can adjust the temp with the dial on the front and the boiler acts accordingly heating the water to about the temp I set then stopping. The first few minutes were definately less active on the gas front and then it kicked in full pelt after a while.

I have decided to order a new NTC as for the sake of 15 quid I can find out if this is faulty or not.

willl let you know how things progress

 

[The831Bunny]

Filter blocked at the brass tee on the flow pipe and/or plate exchanger blocked on the primary side. The filter is a bitch to remove!

Bunny

 

[hairyfingers]

Hi all

so an update:

I took off the plate exchanger and flushed it though with a pressure washer and some DS40. A bit of cr*p came out and it now has a good free flow of air through all its passages - although it didn't seem to bad before

I replaced the NTC.

unfortunately the hot water still overheats to 85 then safety stat kicks in.

what I have realised however is that the front dial that selects the temp of HW does actually make a difference in that if I set the dial to 40 degrees the boiler heats the HW to 65 degrees. so basically the HW is heating up to about 25 degrees more than where I tell it to. therefore as long as I don't set it past 60 degrees then the safety stat never kicks in and the boiler happily keeps hot water flowing.

The CH heats up to within 5 degrees of what I set it to - should it be more accurate than this or could this be hinting that the pump is running slow?

So here is my current thinking:

- it could be the PCB is sending wrong info
- it could be the pump is running slow
- it could be the filter that bunny831 mentioned although bunny mentioned is it a bugger to get off so any tips on how to get it out would be appreciated.
- or maybe the boiler is set to the wrong gas rate

hmmmm so many possibilities.....

any other wisdom to add?