Boiler not working properly...any ideas?

[RandomTask23]

Hi, Can anyone help to diagnose the problem with my heating.

I have a Veissmann Vitodens 100W (under 3 years ago).
Over the last week days the performance has dropped to the point where our heating and water are only luke warm at best.

From observing the boiler for a while this is what is happening:
1. Temp on boiler falls to about 30-32°C
2. Boiler fires (only low power. 1 bar out of a possible 5) until temp reaches 50-60°C (depending on temp setting of boiler) (this takes about 30secs)
3. Burner switches off
4. Temp cools back to 30-32°C...and cycle repeats

After the burners switches off the pipes near the hot water tank upstairs click/tap for a while. This has got a bit louder and more frequent over the last few days too.
I've checked the magnaclean system we have installed (minimal build up) and bled all the radiators (only small air in the highest rad) and this has not made any difference.

We are still under warranty with Veissmann so I was planning to call them this morning...but I'm not actually sure if the problem is the boiler or some other component in the system.

Any ideas?
Thanks in advance.

EDIT: Forgot to add that I also tried cranking up the wall thermostat to 30°C to see if that made any difference...it didn't. The same cycle continued.

 

[HERTS P&D]

Well, what happened when you called them out?

Andy

 

[Agile]

I am sure they found the boiler was fine and a lack of circulation !

Perhaps something turned mostly off or a failing pump.

If he had quoted the flow and return temperatures then we could have deduced something!

I wonder if he has had the boiler serviced annually?

Tony

 

[RandomTask23]

UPDATE:
Everything is working fine now! Although no actual problem was found I think your idea of a circulation problem must have been right.

Our heating engineer checked the pump (working fine and clean as a whistle) and did a few other tests to check for blockages and to look at the general condition of the water in the system. Nothing had changed since the last service 6 months ago and everything looked very clean.

He thought it might be a problem with the flow/return sensors in the boiler causing it to shut off too soon as a couple of these boilers he'd fitted around the same time had developed this fault.

Since the boiler was still under warranty I called a Veissmann engineer out to have a look.
They couldn't come for a couple of days but in the intervening time I tried increasing the thermostat temps on the cylinder and wall sensor to get a bit more heat somehow. This was actually very successful in increasing the rad and water temps.

After putting them back to the previous settings the next day I was expecting the problem to reappear but everything has been fine since. (Perhaps the extra flow of having to work a bit harder helped push something through the system?).

When he arrived later that day, the Veissmann engineer checked the boiler over, including resistance checks on the sensors, and unsurprisingly everything checked out.

That was Friday and it's been fine since then. So I'm glad it's fine but kind of wish I knew what had resolved it, incase it ever happens again.