Worcester greenstar 40cdi cuts off 2-3 mins 90 temp

[Uzair]

Hi,
im not very familiar with central heating and water systems.

We have had a problem with our boiler where it starts up temp gets hgh so it cuts of temp reaches 90 then drops down to 30/40 and the same cycle again. We had an engineer out who had a look tried to fix it for 2 hrs and then left. saying we need a senior engineer and u can still use the system. We put our heating and water on again and it worked for an hr with the symbol for syphoning? or somthing? once it started up properly it made some very loud noises above the boiler and came up with u2 u3 u4 u5 u6 u7 on the display.

called another engineed in and he said will take to long to look at so senior engineer will come back tmrw and have a look at it. Anyone have any idea what this might mean? as the engineers seem to have little or no idea at the moment.

From reading other forums is it the heat exchanger? it has worked fine for nearly 4 yrs now. does anyone know what the u2-u7 mean?

any help appreciated

 

[boilerdoktor]

The u codes mean the boiler heat isn't getting away from the boiler! Is it a conventional boiler, system or combi

 

[Uzair]

its conventional

 

[simond]

The U codes say the boiler is overheating.

It sounds like there is an airlock, pump failure or a blockage (frozen pipes?).

If the return temperature to the boiler is cold this is a key sign.

I doubt the heat exchanger is blocked unless you have had similar problems elsewhere in the system.

 

[simond]

The siphoning period you mention is the WB infuriating condense trap filling mode which the boiler goes through every time it is fully powered off then on at the supply.

This is normal.

 

[bengasman]

Have you tried running on ch ONLY and dhw ONLY?

 

[Uzair]

Thanks for all the posts.. i havent tried it as i dont know what ch or dhw means? sorry not familiar wit heating and boilers at all.. we just phoned the engineers again and they are coming tmrw just hoping it can be sorted out as its freezing with no heat or hot water. The pump is only 2 yrs old and the first engineer said that seems to be working fine... mayb a blockage or airlock might be the problem thanks simon. If they cant figure out whats wrong then i can atleast mention these possibilities.