central heating system tripping

[danm]

I am hoping someone can help me with a problem which is driving me mad!! I have a Vaillant 28e condensing boiler installed for 3 years +. I have had an ongoing intermittent problem for a number of years-possibly since it was installed.

The system runs fine for months ans then all of a sudden the boiler starts to trip out on fault F26- maximum delta t. This i believe is when the temp differential between flow and return is too great and it does seem that the return pipe is not getting very hot!!

The problem has appeared again today. I have had plumber out to look at who have fiddled around with the system-changed the pump-cleaned the system out and they have eventually managed to get it working but always only for a period of time.

Today I have drained the system down - water is clean enough to drink, but it still trips out. I did get some of the radiators hot for half an hour before it tripped again. I reset and it very quickly trips out on the same fault.

Any ideas would be gratefully received.

 

[gasline]

Did you manage to sort out this problem? I appear to have the same.

 

[Beerlover]

Is the boiler you have an eco max pro 28 ?

Was the sysytem very dirty before the plumber sorted it out ? and is this on an open vented system? Was a new pump fitted with the boiler?

 

[45yearsagasman]

You've said that the return temp does not get very hot.You need to check the flow/return diff temp.Approx 20c for a modern boiler.If this TD is excessive your flow rate accross the heat exch is slow and needs sorting.