Rads heat fine, but no hot tap water?

24 Jun 2006
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United Kingdom
I have a gas boiler made by Valliant. Its the on demand type, so no water storage, it heats as you request water (forgive me, diy noob)

Anyway, when we moved in it seemd to work fine however a few things dont work now.

The pressure guage and temp guage all read zero, i dont know if they're broken but I get hot water so the temperature guage is lying.

The problem I have is that the boiler heats the radiators fine when on heating+tap mode. The taps provide hot water also.

But as soon as you put it on 'tap only mode' the flames turn off and the tap goes cold. this was only happening for upstairs (ie, no hot water up there unless radiators on) but now even the kitchen one right next to it doesnt kick in the boiler when turned on.

This has slowly been getting worse week by week.

Now, I cant even get any hot water when the boiler heats the radiators, as soon as i turn the tap on the boiler shuts off

The sticker on the boiler door says to check the guages and if needed top up the system... love to know how to do that.

So, to recap, when I moved in, both tap only and radiator+tap modes worked fine.

A few weeks ago the tap only function stopped working for upstairs. If i wanted hot water the rads had to be on.

Last week the tap only mode stopped working for downstairs too. Now for any hot water the rads had to be on.

Now, today, I get no hot water on any mode. The rads heat fine but the boiler shuts off as soon as the hot tap is turned on. Turn off the tap and the boiler fires up again

Is this a pressure issue?
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Firstly you have to repressurise the boiler, see FAQ on this site.

Next you have to get someone to repair or replace the failed diverter valve. This will depend on the model of boiler you have. Vaillant, like Ford cars, made a lot of different models over the years.

Tony Glazier
Vaillant-Ford :eek: I thought the quality of the boiler was better than that :LOL:
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yeah i drive a ford, it works better than that!

Whilst you dont pressurise your boiler I do hope you top up the rad water in your Ford sometimes.

Have you repressurised the Vaillant yet?

Have they got rid of that dreadful cement works to the north of Rugby yet?


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