Vailant boiler no hot water

[evedawn]

We have intermittent hot water. The taps run warm (not hot) for a few secs then ice cold then warm then cold etc. The following have been replaced: sensor, heat exchanger, and a small pipe to the "bladder". Today theplumber is replacing diverted valve. If this doesn't work any other ideas?! ! The boiler is not showing a fault code.

[AlBags]

The small temperature sensor/switch (if it has one) on the output side. Usually strapped/attached to an internal pipe somewhere. About 1 cm diameter) Check the manual. Some do not have this type of switch. If they fail, you can get this type of problem.
Worth checking.

[evedawn]

Thank you both of you for suggestions !

[evedawn]

Plumber here now. Replaced diverter valve but still same prob.says it has noPressure differential assembly. On this boiler. Has replaced micro switch. What next? Help abers

[AlBags]

Is there no manual anywhere?
Is there a thermal switch on the pipework?

[iansterling]

its the diverter valve diaphragm just change the seal for about £10-£15 rather than change all the valve assembly

[evedawn]

Yes the plumber has gone through manual entirely. Entire diverter now changed. This vailant combi should show a fault code too but showing as tho nowt is wrong! The plumber / heating eng is very competent (has done lots of boiler work fir my husbands co) but he is stymied!

[evedawn]

Oh and the thermal switch has been replaced albags. Boiler is seven yrs old and has been serviced yearly etc

[AlBags]

Is the burner igniting, flaming up and staying like that til cycle is killed and tripped? Any chance of gas pressure problem tripping main burner?

[evedawn]

Ecomax824. Yes it's staying ignited

[AlBags]

We're all clutching at straws now ...
Yes .. OK .. So pump is definitely circulating and all rads working ok.
Diverter assy replaced.
System pressure charge ok? for sure? Sensor for pressure?
Thermal switch OK.
Gas pressure ok.

[AlBags]

Taking a look at manual too.

[evedawn]

Oh and ... The small heat exch replaced (this boiler has a large and a small h. Exch) the way this is going we nearly have a whole new boiler in replacement parts!