Vaillant EcoMax 835 DHW

[Neilsspot]

Hi

new to this site but need some help.

I have an Ecomax 835 installed for many years and I have noticed today that the DHW seems to cooler than normal. Went and checked the boiler and with the DHW thermostatic dial set in the mid point the boiler kicks in o.k when the tap is run. Thought I needed to turn the thermostst up to increase the temperature, now i have it on maximum but the temperature doesn't seem to have increased much. At first it ran really hot once but now just seems luke warm like before.

looking at the forum it probably needs a flush through the heat exchangers ? When the boiler runs initially it runs full bore then modulates back but even with the tap on full flow it doesn't seem to fire up to full bore again?

When i disconnected the HTC at the DHW outlet the boiler kicked into full gas flow and the water ran nice and warm. Boiler indicating 79 degrees. Is this normal or is it indicating a fault with the HTC which is limiting the normal temperature output. I guess when disconnected the PCB is sensing infinity resistance so it will go to max temp ????

The diverter valve seems to be modulating o.k before anyone asks. Any help would be appreciated with two days to Christmas and her worrying my head now.

Thanks

Neil

 

[Agile]

It does sound as if the secondary heat exchanger is rather blocked.

But a confirmation of that would need measurement of the flow and return temps together with the DHW temp after setting to the spec flow rate of about 13 li/min.

Tony

 

[Neilsspot]

Thanks for the quick reply.

With the tap at full bore I'm getting about 10l/min.

Flow in at 71 degrees

flow out at 57 degrees

That's with the temp stat turned right up to max.

Sorry about before (HTC meant NTC). Is the NTC working correctly then ?

Thanks

Neil

 

[Agile]

Those temps are about right but both a bit high. So its not significantly blocked.

But it is possible the surface is coated with a poorly conducting layer.

The next question is what is the temp of the DHW at that flow rate.

Can you measure the gas rate at those conditions? See the FAQ on this site. I expect it will only be about 25 kW which is lower than it should be.

Tony

 

[Neilsspot]

Looks like I need a better thermometer to measure the temperature. The wife's fancy digital medical thing just died on me.

To measure the gas flow do you mean read the gas meter as the boiler is running ?

Ta

 

[Neilsspot]

Its burning 28kw at the 10l/min flow rate.

The boiler setting via the diagnostic code is set a 27kw which is the maximum for the boiler.

I guess allowing for the inaccuaracy of a mechanical gas meter against a boiler it is fairly accurate don't you think ?

Sorry can't tell what the temperature of the DHW is. All i know is that it is more than 42 degrees. The thermometer didn't like it after 42 and gave up the ghost.

 

[Agile]

The gas meter is very accurate!

You cannot read the input power on the boiler! You set the OUTPUT power in d1.

Did you get the 28 kW INPUT power from the gas meter readings as instructed on the FAQ?

If the DHW is over 42 C then it seems to be working pretty much as expected.

How long can you keep your hand in the hot water?

Tony

 

[Bunnyman]

It sounds more like the knobs snapped tony! When ur runnin hot water what does the flow temp go up to on the display when the ntc is connected?

Untitled

• Bunnyman
• 26 Mar 2010
• 499

 

[Bunnyman]

If the temp goes to 79deg that's normal an if the waters hot then the dhw ht exch can't be blocked

Untitled

• Bunnyman
• 26 Mar 2010
• 499

 

[Agile]

Hi

Thought I needed to turn the thermostst up to increase the temperature, now i have it on maximum but the temperature doesn't seem to have increased much. At first it ran really hot once but now just seems luke warm like before.

Thanks

Neil

I interpreted that to mean that it has increased " a little" and so the knob shaft is OK.

OP, does the DHW knob make ANY difference? The knob shafts can snap and not turn the pot on the PCB. Thats a safety feature to prevent damaging the pot!

Tony

 

[Neilsspot]

Sorry for the late reply, just got back from the Christmas visiting etc.

With the DHW knob wound right up the display shows 71 degrees. The actual temperature of the water is not 71 (still haven't got a thermometer so not sure what it actually is yet). When I wind the knob back you can feel that the temperature gets cooler and the display corresponds with the backing off adjustment.

It assume that the NTC is what actually gives the feedback to regulate the temperature ? This is why I asked that when it is unplugged the water runs to full temperature, surely that means the HTC is giving a false signal back to the PCB etc. Any ideas on what the resistance figure should be for the HTC at various temperatures etc. ?


I'm just in the process of draining down the system to see if much crap comes out. It all looks very clean so far. I know this won't clean out the secondary heat ex but at least it means it's clean as possible without a power flush etc.

Ta Neil