worcester Bosch 28si II fails after about an hour

[rogers827]

Hi,
my neighbor has a WB 28si II that will run for about an hour before stopping. The red light flashes slowly and when reset the boiler will run again for about the same time (maybe a little less). It has been doing this for a few weeks now.
I understand that slow red flashing light indicates either an ignition fault or an overheat problem but every time I check the boiler for them I can hear the igniter and it always lights, additionally I do not think its the gas supply as it runs okay for so long.
Also I am uncertain about it being an overheat problem because it runs for a good while before it stops and they can always reset it fairly quickly.
Any advise would be most welcome

Rog

 

[clf-gas]

It is an over heat problem but you need to find the cause.

Could well be the heat ex partially blocked.

 

[superdupergasman]

or a slugish pump or a dodgy thermistor

 

[ChrisR]

Or a GV solenoid sticking when it's warm.
I have some sticky labels which record how hot they've ever got - useful for these horrible faults.

 

[rogers827]

Guys - thanks for the responses - food for thought.
Please correct me if my thinking is wrong but I would have thought a partially blocked Heat Exchanger would cause an issue with the hot water supply - as far as I know that side of things is okay.

Regarding a slugish Pump - the house seems to heat up quickly so there does not seem to be a problem there.

As for the thermistor and the Gas Valve - are there any straight forward ways of checking these out?

 

[superdupergasman]

Well the best solution is to stand infront of it till it does the fault,

Your boiler has a twin pass Heat exchanger so the same one is used for the CH and HW although the water never touches.

A sluggish pump will still heat the house up its just not getting the water away fast enough when the temp gets right up to 80oC.

Gas valve you cant touch, and thermistor is just screwed to the pipe by a clip.

 

[dylan_30]

hi did you ever manage to sort this problem as i have a similar problem. was your problem linked to the hot water being used whilst your ch was in use
dylan