Vaillant Turbomax Plus 828E Problem

Hi all, I am after a bit of advice on a problem with my combi boiler, hope you can help?

The CH has begun taking a lot longer to get the house warm, and the hot water goes luke warm to hot and back to luke warm in a cycle.

I had my plumber over to do a routine service on it and see if he could see anything obvious he says that when the boiler ignites it goes onto the low flame then after a short while it goes to the high flame but after about 10 secs there is a click and it drops back to the low flame, this cycle is continuous whilst ever the boiler is called for heat on CH, and also it does the same cycle on HW. He spoke to Vaillant help desk but they had not heard of this fault before.

Has anyone experienced this before?

Gas pressure is in spec

Forgot to mention there are no fault codes stored

Cheers

Ade

Could it be flame picture out of sync i.e. electrodes incorrectly gapped - should be 4mm or gap of £1 coin.

Had similar problem and gapped accordingly, which solved problem.

Hi Guys

Just want to post back letting you know that the fault was due to the Pump being sludged up running slow, the engineer said the effect of this was the boiler was 'kettling' due to lack of flow round the system. New pump fitted and now both CH and HW working perfect

Cheers
Ade