Tap water gets too hot when radiator turn on

[rockinter]

Hi,
I have combi vogue gen2 boiler. The tap water temperature is okay when we run without radiators on.
When the radiators are on the tap water temperature gets too hot.
The tap water is at temp 45 and radiator temp at 60.
Is this normal?

 

[RandomGrinch]

Yes, I believe this is normal. It certainly happens on my system!
When the radiators are running, and then you turn the hot water on, the system stops feeding the rads and has a huge amount of excess heat to dump. This naturally ends up overly heating the hot water.
Once the excess heat has been removed, the hot water should return to the set temperature.
I hope that makes sense.

 

[DP]

Yes, I believe this is normal. It certainly happens on my system!
When the radiators are running, and then you turn the hot water on, the system stops feeding the rads and has a huge amount of excess heat to dump. This naturally ends up overly heating the hot water.
Once the excess heat has been removed, the hot water should return to the set temperature.
I hope that makes sense.

It is more a case of primary water ( that heats the radiators) passing through the plate heat exchanger in small quantities ( that takes the heat from the primary loop to heat incoming cold water) so that the water that is sitting in the plate heat exchanger is at primary flow temperature OR the preheat is elevating the temperature to high point. When you run hot tap, boiler goes to max power and cold water temperature is elevated to HW stat setting

If heating off, does the water still gets quite hot? What happens if you lower the CH temperature on the boiler.

When running hot tap fully flow and full setting of HW thermostat on the boiler, what is the delivered hot water temperature.

Cold water is around 18 degree C at present, may well be 20 for you. Boiler will raise the temperature by 35 degrees at max HW setting, gas rate being correct and system not fouled. Often see 36 degree C rise- you should be able to get hot water temperature of 53 degree C leaving the boiler. This test might show discrepancies if target temperature cannot be achieved.