Vaillant Turbomax PLus 824 cycling between S.10, 13, 14

[mmockett]

Hi guys,
We recently had our boiler repaired as a previous owner left one of the valves open and the pressure was constantly rising. The repair-man closed the valves and now pressure is stable at 1-2 bar. But ever since, the boiler has been failing to remain hot when running the tap / shower. From what I can tell, it ignites, burns for a bit and then goes out, starting again. The temperature fluctuates between about 45 and 80 degrees within a few seconds, and when it goes up to 80, it turns off / when it goes down to 40, it turns on again. Means that we get a little spurt of hot water, and then cold again... It's showing S.10 / 13 / 14 when the tap is running, and cycles between 13 and 14. Any idea what could be the problem? I've read a few other posts on here, and there are some similar circumstances, but no solution yet. The boiler is a Vaillant Turbomax Plus 824.
Thanks for your help,
Max

 

[Beerlover]

It sounds like a blocked plate heat exchanger.

However it could also be a weak pump, blocked main heat exchanger or the flow ntc may be shorting on the casing (rare fault).

If attempting the repair yourself, use plenty of silicon grease when refitting the plate heat exchanger and make sure it is locked in before restoring the supplies to the boiler.

It can be a pig of a job so you might want to get a pro in.

 

[mmockett]

Thanks BL - sounds like this one's above my pay-grade. I'll put in a call to the Vaillant guys as I'm covered for the year after last week's fiasco. It's odd that the problem only arose after the engineer checked it over - makes me think it isn't a hardware problem, but I'll let you know what he says for future reference.

 

[Agile]

Leaving the filling valve open causes new oxygen to enter the system this rusts the inside of the rads and flakes of oxide fall to the bottom.

As heating is used those oxide flakes get carried round the system and they block the plate heat exchanger.

The plate needs to be replaced or cleaned ( we clean as thats cheaper for the customer ) and then some action taken to remove any further dirt.

That cleaning could range from flushing the system through with clean water, chemical cleaning, power flushing and/or adding a mechanical or magnetic filter.

Exactly whats the best compromise depends on just how dirty the system is and that choice depends on the skill of the engineer.

You can see what they do but Vaillant should not deal with these aspects as they are not a consequence of the repair that they did. Most insurance backed schemes specifically exclude any problems caused by dirt in a system.

Tony