How can I test my DHW Heat exchanger?

[ChrisR]

If that's 130 to 222 on the last 3 digits on the meter that's a bit low(29.5kW input I make it). Maybe the boiler is cutting itself down because it thinks it's hot enough, but 70 isn't high enough for that.
70 in , 60 out
6 in, 25 out
Would have expected better transfer than that.
19 degree rise on 10 l/min is 13.25kW.

a) ??? primary side of main heat exchanger scaled (too much energy is going up the flue, (29.5 / 35.5) * 26.6 = 22.1kW)
b) ??? primary temperature sensor (70 is too low)
c) ??? gas valve pressure (worth checking)
d) ??? primary side of secondary hex scaled up (Inadequate transfer)

Which type of HEX is it??

 

[RogB]

Not sure I can tell you what type of DHW Heat Exchanger it is but it looks like an aluminium flask, approx 200mm high & 100mm diameter.

Also ChrisR, I am very interested in your calculations can you explain in a little more detail how you got 29.5Kw input, the 13.25Kw for the water heating and 22.1Kw?

What drop in temperature would you expect across the heat exchanger?
What would be an acceptable input temperature? If the sensor has been changed but made no difference, what else controls the input temperature?

 

[DP]

If the HW HE was scaled up, I would expect the burner to downsize. Cannot see the burners running full wack with no heat going to radiators or fraction transfered to cold water.

What is the burner pressure? This boiler has a habit of running on lower burner pressure sometimes if it has not been serviced as described by Vaillant.

 

[RogB]

I don't know what the Burner pressure is, can I test? Sounds like a CORGI task.