Hot water circulates to radiators but nil hot water to taps.

[lesbrack]

Yes I have done a search but so far cannot find answer.
Potteron Netaheat MK11 10 - 16. Probably very ancient.When central heating valve is turned to its usual 90 degrees 'on' position on the cylinder the hot water circulates to rads normally - hot water immersion heater turned off.
When hot water to taps only is required the gas boiler ignites as usual but the water temp to taps is barely lukewarm if at all.This happens even though the heat setting on hot water cylinder is turned to 'max'.At the moment we are using the electric immersion water heater on the the same hot water cylinder to heat the water for the taps.
Appreciate any help with this.

 

[ChrisR]

We need to know what all your bits are. CHances are you have a "2 port" motorised valve on the HW which isn't opening. Another search on some of those words should find plenty

 

[lesbrack]

This problem turned out to be 'simply' a stuck pin/needle on the Drayton thermostat valve on the hot water cylinder.The Potterton Netaheat Mk2 boiler may well be 25 years old but the problem was not there. A light tapping freed the pin/needle part of the valve- it popped up and the water began to flow correctly to the hot water taps again.
Hoping that this will help anyone.