The Halstead ace boiler I think is typical.
There is a 'diverter valve' which is movable to the left. When moved it diverts the water from CH circuit to the HW circuit (heat exchanger)
At the end of its travel the valve triggers a microswitch.
You can see a faulty micro switch or a sticky valve and you have problems.
But the main problem is related to the 'diaphram operated switch Assy'.
It's this Assembly that moves the valve. How?
The Diaphram has mains water on both sides of it. When the hot tap is opened the pressure on one side is reduced. This allows the pressure on the opposite side to push the valve across. If this diaphram is split/holed the higher pressure water passes to lower pressure side. The result being the valve does not move or may move slightly, but not sufficient to light boiler.
This I believe accounts for many problems when no HW on a combi
The Halstead Ace is the best kind of diverter valve.
The most common type as used on Worcesters have a manifold section which has to follow the DHW bit under spring pressure and often gets stuck but you cannot see what its doing.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local