Combi boiler - hot water isn't very hot, but radiators work OK

[iceland_potter]

my Ravenheat Combi boiler had a problem recently where it was on zero pressure, so I turned a plastic tap underneath which was connected to a felxible pipe, which seemed to let more water into the boiler.

The radiators now all work full heat, but the hot water isn't very hot, and the hot water isn't hot at all when the switch is switched from central heating and hot water to just hot water. I've tried varying settings on both thermostats.

It seems like something's wrong as the boiler used to be fine to pump out hot water when the switch is just set to hot water.

Pressure is about 0.8 bar cold and i'm not sure what it is when hot but its over 1 bar.

Has anyone got any ideas please before I call out a plumber?

Many thanks.

[Ed Sirett]

It's very likely the diverter valve. Switch the CH off, run a hW tap, if the boiler fires and the CH flow pipe gets hot the that's really all the proof you need.

[Stuart B]

On the assumption that this is not a troll.....The plastic tap you refer to is the control for the Filling Loop to increase the pressure in the boiler .The instructions that were left by the installer ( They were weren't they?) will explain all ( You have read them haven't you ??) .

AIUI the pressure should be read when cold and not hot so it might be that you need to put more water in when it's cold .

Is there not a temp control for the HW so you can increase it to a temp that suits you ?

[iceland_potter]

Thanks Ed and Stuart,

Ed - sounds like it could be that, although when I turn the hot tap on, there is immediately a burst of hot water, then it goes lukewarm at best for sustained periods of time.

Stuart - Why would I be a troll? I have a problem with my boiler, so I posted to a diy usenet group, please explain why you think I may have been a troll?

I have put more water in the boiler from cold though to raise the pressure to 1.2 bar, this seemed to work for a bit then after a day or so I'm left with the lukewarm-at-best problem as described.

[Ed Sirett]

The most likely failure modes are:

1) The water flow diaphragm has partly split is becoming less sensistive and effective, whilst it still switches the boiler on it is not strong enough to move the valve fully to the DHW position. 2) Due to anyone of a number of problems the diverter valve is too stiff to shift to the DHW position.

HTH

[iceland_potter]

Thanks Ed,

I ended up getting a gas boiler firm out under a caveat of my home insurance who took a look. After much tutting he decided a whole diverter valve replacement was required. He's due to come tomorrow, lets hope this sorts out my boiler.

[iceland_potter]

Just for completeness, thought i'd post. The diverter valve was replaced and boiler sorted.