Vaillant 824/2E, low DHW temperature

[Pete964]

Hi All, I have above boiler. The problem I have is the temperature of the hot water at the tap is 37deg C but the boiler reports it to be 76 ish.

The CH is fine and heats up quickly.

I had the heat exchanger off last year and descaled it after it got noisy and the water was tepid.

The boiler is about 10 years old and since I cleaned the heat exchanger last year it improved things a little but its getting worse again.

I find it hard to believe its scale again, the system has been inhibited with x100. Iv just drained it today and dosed it up with F3 but no effect yet.

Any ideas folks?

 

[Gas2Air]

As a prat as you are, have you checked, thermistor values? Gas rate on HW and flow rate?

Your blr is scaled, possibly passing to CH, are you able enough to check this?

 

[Pete964]

with the DHW on full:

the (mains not LPG) gas rate is 0.037m cube / min
water 9L/min

the water into the DHW heat exchanger from the main ex. is 60deg. out is 47deg. (checked with a probe on the appropriate pipe)

main cold water supply is 5deg. and the DHW is leaving the exchanger at 36deg.

the boiler is reading a water temp of 70deg to 72deg after 3min of run on its display. I can hear it regulating the gas to maintain the 70deg ish. (is this the temp as it exits the main heat exchanger?)

the DHW exchanger was de-scaled last summer with kettle de-scaler and looked clean although not like new, and was a complete pig to get on and off.

 

[Pete964]

Any more thougths on this, anyone?