Central heating problem ?

[Zen]

Central heating (Gas) works fine in Heating/water mode but when I switch to heat Water only mode the burner ignites but goes out after 2 minutes.Thermostat problem or what ?

[nedflanders]

what make model is your boiler ? is your water hot or cold ?

[Zen]

Some sort of Baxi,model unknown fitted 3 years ago.Water is cold .

[gen2]

When ours repeatedly switched off after a short time it was because the pump wasn't turning.  If it is the same pump used in both heating modes then mabe it isn't receiving a switch-on signal when you choose to heat just the water.  Another possibility is that an electrically operated valve is not opening.  In either case, the heated water is not leaving the boiler and so it switches off as soon as this small volume of water gets too hot.  Therefore I would say that the thermostat is working OK.

[Zen]

Great answer,thanks.