Delay in Boiler Firing

[cleanpairofheels]

Great this web site exists to handle an issue for me...

My daughter has just brought a flat with an old gas fired Vokera boiler, that has an "S" configuration with independent heating of water and heating. I know at some time it needs to be changed out for a new boiler, most likely a Vaillant per my own house, but in the meantime a problem that I'd welcome advice.

When I set the heating for either "once" or "twice" at the required time the control panel light comes on and I think the fan comes on in the boiler, and maybe the pump ( a whirring noise anyway). However it takes 15 mins before the boiler actually fires up and it does this pretty consistently time wise. Once running its fine but I wondered if anybody could point me towards the most likely cause.

Note I can't find a room thermostat so I don't think that's the cause.

Comments appreciated.

cpoh

[supremetwo]

You may find details of your boiler here:-
http://www.vokera.co.uk/trade-professionals/manuals-literature/#discontinued

A faulty air pressure switch or a slow-running fan not building up sufficient pressure in the boiler casing?

The latter may also be caused by a casing-seal leak.

[cleanpairofheels]

Thanks for the comments Supremetwo which meant that I was ready to call the local heating engineer.

You were almost right...He found a blockage in the heating manifold which apparently was preventing a satisfactory vacuum being produced - hence the delay in firing. Fortunately that problem is now solved, but sadly there's another issue that has arisen. Don't know if it was pre-existing.

Now on shutdown of the boiler, there's a severe case of pump overrun. (sometimes the pump runs for hours, but it seems to be weather dependent as to whether it does that). A web search indicates a boiler thermostat issue.

http://www.tertullian.org/rpearse/heating/overrun.htm

Does that make sense?

Note that there is no frost stat or room thermostat installed and I've just had the motorised valve on the water system changed out which was another likely cause.

ps. Its a Vokera Mynute 28/96 SE sealed system, with "S" type configuration.

Thanks,

cpoh

[supremetwo]

Thanks for the comments Supremetwo which meant that I was ready to call the local heating engineer.

sadly there's another issue that has arisen. Don't know if it was pre-existing.

Now on shutdown of the boiler, there's a severe case of pump overrun. (sometimes the pump runs for hours, but it seems to be weather dependent as to whether it does that). A web search indicates a boiler thermostat issue. cpoh

A not uncommon fault.

Perhaps the circulating water is running hotter now that the air pressure is correct.

Is that noticeable on the rads?

[Diziet]

No help with the cause of the problem, but Vokera have an offer of a fixed price repair, which I have taken advantage of for my own 17 year old boiler. I paid 257 euro (not sure what the price is in the UK, but it can't be that far different) and this includes all parts. Cheaper than a new boiler, and, although Vokera are not the best, they are not terrible, either.