getting hot water when heating only is on

[wts]

Hi, I have a Worcestor Bosch Heatslave 20/25 (combi boiler). Recently, when the heating is switched on I get hot water despite hot water being switched off. If I only switch hot water on, then I get hot water as expected. Can anyone help? Thanks!

 

[jurassic sparkk]

Diverter valve?

 

[wts]

Thanks, but the diverter valve has just been changed, but didn't resolve it. PCB also got changed.

 

[trojanhawrs]

From the manual.

9.2 The appliance incorporates a three-port, two-way divertervalve which diverts the boiler output to the Heatslave tank inresponse to a demand from the Domestic Hot Water ControlThermostat or the flow switch. The valve is powered open inresponse to a demand from the Central Heating ControlThermostat or a room thermostat, and the boiler output isdiverted to the heating circuit.If there is a demand from both the Heatslave tank and thecentral heating, the valve will give priority to the Heatslave tank.The central heating will therefore remain switched off for a shortperiod of time. This delay will vary depending on the applianceoutput and the quantity of energy required to satisfy thedomestic hot water demand.The Heatslave tank priority can be temporarily overridden toregain the central heating output by turning the Domestic HotWater Thermostat fully anti-clockwise for the duration of thewarm up period. This will prevent the Heatslave tank takingpriority for the tank warm up period of approximately 20minutes and may be found advantageous to give quickerheating to the dwelling when starting from cold.

 

[wts]

I understand what you're saying, but surely I should be able to have the heating on and NOT have hot water if I so choose. My hot water is permanently set to off, but I still have hot water.

 

[trojanhawrs]

It doesn't appear that way. Why do you want the hot water off?

 

[wts]

I don't really but I had noticed that when the heating is on the hot water is always stupidly hot, whereas if only the hot water is on it is as hot as I would like it. I therefore assumed that the heating was affecting the hot water and turned the hot water off to test it!

I have now attempted to understand the flow chart for "Central Heating Mode Only" from the manual, and if I understand it right the 'boiler high limit thermostat' is being activated and therefore water gets pumped to the heatslave tank. Is it right that this high limit thermostat is so often activated?

 

[trojanhawrs]

The way I understand it, the hot water is fed at mains pressure and goes through a heat exchanger in the heatslave tank. So, if the heatslave is hotter i.e. the heating is on, the hot water will be hotter as well. You could reduce your central heating thermostat setting on the boiler to keep the tank at a lower temperature, means your heating will take a little bit longer to warm up. You could also install a thermostatic mixer valve on the DHW main

 

[wts]

Thanks very much for your help!