Glowworm Swiftflow boiler noise

[exploited]

Boiler make / model
Gas Glow Worm Swiftflow 75

Heating OK.
Hot Water OK.
Noise problem.
Problem for approx 8 weeks.
No recent changes to system.
On central heating start up everything OK.
When central heating at working temperature noise from boiler starts.
Noise is a high pitch hum/vibration and lasts for approx 7 sec at the end of a 21 sec heating cycle.
As system continues working the noise gets progressively worse.
If the central heating is on and you use the hot water for any length of time eg run a bath, when the taps are shut off ,the noise starts immediately and continues for a longer period than normal.
First suspected pump bearing but not so sure now after investigation.(listening stick)
Seems more related to possible over temperature maybe?
Any ideas to narrow down possible causes?
How can I check if overtemp is the problem? eg where to test, what readings are normal etc.

 

[Agile]

I realise that you have clearly said quite a few things but the real clues are not there.

It sounds to me as if it might be caused by the gas staying on when it should be off. This 21 sec heating cycle is wrong too, can you elaborate?

Can you turn off the hot tap and see if the flame goes out immediately?

This is a very simple boiler but obviously any faults need diagnosis using careful observation and tests.

In front of the boiler I expect I would see the fault within two or three minutes but over the internet it could take weeks!

Tony

 

[exploited]

I'll try to give you some more detail -
The heating cycle obviously changes with the heating demand but typically when up to temperature the cycle is approx 20 secs on 90 secs off.
With the heating off the gas operates correctly with the taps.
With the heating on and running taps together I guess the water is getting the most benefit from the exchanger. Running a tap to wash you hands say has little effect.
However, when you run a bath for instance and then turn off the taps the boiler continues to run for more than the normal 20 secs since it has to make up for the loss of heat input to the bath water.
Once it completes this extended heat cycle it returns to the typical 20 sec heat cycle.
The extended heat cycle is noisy for the whole length.
However, when you first switch on the system, the boiler is constantly running until the rads are up to temp. There is no noise when going from cold to hot. Hence my suspicion this is tempearture related rather than pump - but then again i'm no expert!

 

[Agile]

I think that I am begining to understand what you are trying to tell me. Its made a bit harder for me to follow because you seem to want to tell me why you think things are happening rather than just whats actually going on.

Reading between the lines to filter out what is actually happenning my conclusion is that the CH power is set too high causing the short cycling.

The noise is more difficult to come to any conclusion about without hearing it myself but my best guess is that there is air because the auto air vent is closed or blocked.

Tony

 

[fitz1]

could be fan.