I have a Vokera combi boiler. The central heating system is working fine. However, when I turn on a hot tap, I can hear the boiler initially firing up, but it only supplies intermittent hot water, interspersed with cold water. This happens whether the system is on heating/water, or just water. Can anyone help please?
Is it an vokera excell 80sp?. It sounds like the flue venturi problem that plagues this and similar models. The boiler needs to know the flues are clear and the airflow is OK before firing up, it does this with a venturi on the flue side of the fan. If your flue gets blocked (rare but happens), or your primary heat exchanger/fan blades/venturi get dirty you get this annoying temperature cycling with the boiler cutting out to pilot only and then going to full flame.
Google vokera flue venturi, temperature cycling etc to get more info.
Cleaning the components is not rocket science, the only tools you need are a no2 posidrive screwdriver, a small needle file(for flue venturi, use gently),a stiff brush (for heat exchanger and fan blades), the manual (downloadable from Vokera) and a bit of a4 paper to stop crap falling into the burners when you are brushing (and of course a vacuum cleaner).
However, if you somehow get it wrong the boiler could be left in a dangerous condition.
It would be a good idea to get it serviced now in any case by a Vokera specialist who should perform various bits of preventative maintenance that will save you more hastle and mean you can ignore the boiler for another couple of years. Phone Vokera (www.vokera.co.uk) for a local approved service man. Corgi generalists can work out very expensive if they don't know the model, and may want to sell you a new condensing combi replacement (Â£Â£Â£Â£).
A proper service will involve installing kit t0019 (if it is indeed an excel model), recharging the expansion vessel, checking burner pressures etc. Should cost around 150quid.