Vaillant ecoTEC not reaching desired flow temperature

[Yikes]

I should say that 3 radiators are usually off unless we have people staying. I tried the pump on setting 3 but it didn't seem to change anything. Should I adjust the ABV?

Mike

 

[Johntheo5]

Yes, might tell something, reduce index until it just starts to get hot.
What make ABV?

 

[Yikes]

It's a Honeywell.

Just one more question before I leave you in peace. Given the age of the boiler (2009) is there such a thing as a software upgrade or replacement control board that might improve its performance?

Mike

 

[Johntheo5]

Can't answer that I'm afraid but worth checking out the pump, if you can lay hands on one of those £15 plug in energy monitors, connect the pump cable into it then get a extension lead and plug it in anywhere just before firing the boiler and then read off the watts, these cheap monitors are quite accurate, you can the read off the pump flow from the pump curves, unfortunately, grundfos do not display the pump power in watts.

 

[Yikes]

I have one of those monitors, that's a great tip. Thanks for all your advice, I really appreciate it. I will speak to Vaillant at some point but they will probably want to sell me a new boiler ...

Mike

 

[Yikes]

Well it turns out that I was on a wild goose chase with this. I was about to test the pump as you suggested when I noticed that the CH zone valve was stuck half open; the return spring in the actuator was broken. I replaced the actuator, set the boiler back to Flow regulation and the Anticycle time to the default of 20 minutes and now the Desired Flow Temperature is being attained and there were only a few instances of microfiring.

Mike

 

[Johntheo5]

Thats great news, but very strange why the ABV wasn't passing as the pump head would/should have been 5M at the reduced flow and the ABV is set to < 3.5M., not sure if your model boiler has a internal bypass, all very interesting anyway and alls well that ends well.
If you have the inclination/time you might do that pump test sometime, if only for interest, all these pumps should come with the power displayed (95% do) as its a great help in trouble shooting and would also have hepled in your case, IMO.

 

[Yikes]

Yes I will check the pump when I get a moment. Thanks again for all your advice, I've learned a lot!

Mike

 

[Johntheo5]

Thought I'd come back to this forum as this is where it originated. I don't know of any model of UPS2 that doesn't have proportional pressure (PP) mode, its pretty useless any way as far too low but could account for those low readings, You should get 22 watts reading on your setting of speed 2 even with the pump discharge valve closed, it is strange that the EM reads OK on other items but not apparently on your pump. I have used my monitor on numerous Grundfos pumps and all read exactly as per pump curves.

 

[Yikes]

Thank you for explaining that. When I get home later I will try to measure the pump power again. I know the meter is OK because it measured down to 1Watt on another device.

Mike

 

[Yikes]

OK after a couple of days away I started again with a clear head and this time got sensible results.

I switched off the boiler, connected the pump to a separate supply and operated the zone valves manually. The results were the same whether HW or CH was selected:

I - 29W
II - 43W
III - 56W

PPI - 9W
PPII - 10W
PPII - 11W

Mike

 

[Johntheo5]

The PP curves seem pretty accurate but can't make sense of the speed curves as the max pump powers are 23W, 37W & 47W for speeds I,II&III and you are reading 29W, 43W & 56W.

So based on a PP3 setting and 11W equates to a head of 1.6M @ 8.4LPM (0.5m3/hr), this would equate to a 5.1M head @ 15.0LPM, (0.9m3/hr),in turn this maps fairly close to running at speed 3 but power would be 46W, so best guessestimate is that the pump on speed 2 is pumping ~ 13LPM to15LPM @ a 4.6M to 5.1M head.

 

[Yikes]

Thanks for this, but not sure what to do with it!

Mike

 

[Johntheo5]

I should have asked you to run the tests as well with the pump discharge valve shut on those 3 fixed speed settings, you might try that sometime.
Is the burner still cutting out with the same symptoms, ie the requested flow temp falling off to zero with consequent recycling?, if so is it possible to change the OT requested flow temperature to simple target flow temperature for a few days?

Also run test with pump discharge valve opened but all zone valves shut, then on say speed 2 only, if power hasn't increased from closed valve power, slowly reduce the ABV index until the power increases, at least this might give some indication of what head the pump is operating at, on speed 2.

 

[Yikes]

I should have asked you to run the tests as well with the pump discharge valve shut on those 3 fixed speed settings, you might try that sometime.
Is the burner still cutting out with the same symptoms, ie the requested flow temp falling off to zero with consequent recycling?, if so is it possible to change the OT requested flow temperature to simple target flow temperature for a few days?

Also run test with pump discharge valve opened but all zone valves shut, then on say speed 2 only, if power hasn't increased from closed valve power, slowly reduce the ABV index until the power increases, at least this might give some indication of what head the pump is operating at, on speed 2.

Sorry but what is a pump discharge valve? Do you mean the gate valves either side that shut off supply when removing the pump?

On the graph above (13th April) the OT was 6C and the heat curve was 2.5, giving a desired flow temp of around 60C. Under these conditions the desired flow temp dropped to zero periodically causing the burner to cut out.

This afternoon the OT was 15C and I'd lowered the heat curve to 1.5, giving a desired flow temp of around 30C. However, the minimum desired flow temp is set to 45C which overrides the heat curve, and in this case the desired flow temp didn't drop to zero but the burner still cuts out and the microfiring has returned:

BTW the controller is still in Thermostat mode.

Mike