Boiler always reaches around 3 on the pressure guage causing water to come out overflow but gradually settles down and stays around 1. It does, however always go to 0 when it goes off and has to be topped up every day. The problem is that once it heats up the rads. it cuts off for about 1 min or so then fires up again for approx. 10 secs then cuts out again,then the fan comes on, then fires up again for another 10 secs. There is no time that the boiler seems to rest it is a constant go on all the time. Recent replacements have been heat exchanger, pressure switch and a perished rubber on the diaphram. Any clues?
Linda

Linda Dalrymple, June 2007

Thank you GC Crell and c for getting back to me so soon with your advice - will let you know if this solves our problem.

Linda, June 2007

This appliance design incorporates a pressure vessel sighted behind the combustion chamber, its designed to take up the expansion of the water in the system when heated. It is devided into to halves by a diaphram, one side being filled with water from the heating system the other with air at a dedicated pressure usualy around 1bar. If the vessel is devoid of this air cushion when the water in the system is heated it has no where in which to expand as air is compressable and water is not this causes increased pressure within the system, at around 3bar of pressure a safety valve designed into the system will release the excess pressure down a relief pipe to outside.
I suggest that either the air pressure within the vessel is deminished or that the diaphram has failed.

G C CRELL, June 2007

Get a Vokera approved service engineer to do a standard service. Phone Vokera for a local man.(www.vokera.co.uk).

I would guess your problems would all be resolved with a competent standard scheduled service.

Pressure variation with the central heating on are due to the expansion vessel being flat - standard service. Get it fixed, regular venting could cause a permanent slow leak from the pressure relief valve requiring an expensive replacement.

The pressure switch (I assume the air pressure switch) seldom goes wrong, the thing that it connects to needs regular careful cleaning for the switch to operate properly, again part of a competent standard service.

Ditch your current Corgi man and try someone recommended / trained by the manufacturer, who knows the quirks of your make and model, and save yourself more grief and expense.

c, June 2007