DHW supply from Vaillant turbomax 828e

[diddlepara]

Hi,

We have a combi boiler supplying dhw and c/h to our 4 bed, 2 bath house. The boiler is in a cupboard on the first floor bathroom and supplies shower, bath and sink.
There is an attic bathroom with bath and sink, and a kitchen sink on the ground floor. Recently the dhw does not fire up if kitchen tap or attic hot taps are turned on. If we
leave one of these taps on and turn on a hot supply in the main bathroom then hot water will be supplied. Turning off one of the main bathroom supplies whilst leaving kitchen or attic taps on and this will turn the boiler burner off.

Any ideas on why this has started happening ? Boiler has behaved very well over the years and only problem was the expansion vessel inside the vaillant failed so my plumber fitted remote expansion vessel with gauge and c/h has been fine. Cold water is pressure at 1.4 bar, won't fill up any more. The water pressure incoming at outside tap is just under 2 bar.

Thanks,

Diddlepara

 

[John.g]

As long as any hot tap flows > 3.0LPM then it should fire up, probably requires a new diverter valve.

 

[diddlepara]

As long as any hot tap flows > 3.0LPM then it should fire up, probably requires a new diverter valve.

Hi John, thanks for getting back. Yes, flow rates for the hot taps in attic are bath 2.25LPM, sink 1.75LPM. Ground floor kitchen tap hot side 2.5LPM. Meanwhile in the main bathroom the hot sink tap is 3.25 LPM. All the cold taps are fed by mains supply and attic are 2.25 and 2.5, kitchen tap 4LPM and main bathroom sink 3.25LPM.

Is this still a diverter valve problem, either replacing or cleaning out along with flushing the boiler and system?

Like me, with age, I need a good flushing out for all my bits to function...

Thanks again,

Diddlepara

 

[cjg]

may need new dhw flow switch.

 

[John.g]

Hi John, thanks for getting back. Yes, flow rates for the hot taps in attic are bath 2.25LPM, sink 1.75LPM. Ground floor kitchen tap hot side 2.5LPM. Meanwhile in the main bathroom the hot sink tap is 3.25 LPM. All the cold taps are fed by mains supply and attic are 2.25 and 2.5, kitchen tap 4LPM and main bathroom sink 3.25LPM.

Is this still a diverter valve problem, either replacing or cleaning out along with flushing the boiler and system?

Like me, with age, I need a good flushing out for all my bits to function...

Thanks again,

Diddlepara

I think 2.7LPM is the minimum requireed so even the main bathroom hot sink tap at 3.25LPM might be marginal, does the boiler fire up with this one only, open?.
I think your boiler's diverter valve is electrically changed over via a aqua sensor so this may be the most suspect as pointed out above but the flow rates are abit on the low side from a sole tap.