Noisey Central Heating Boiler

[tclarke]

I have a fully pumped system with an Apollo 30/50b boiler and in 12 years use it has only had two faults. The first was a faulty thermocouple and the second a faulty pump. They were fixed.

It has been OK now for 2 years but recently it has become very noisy, here is the story:

The boiler stat is set to LOW or HIGH

The pump speed is set to HIGH

The programmer is set to MANUAL

When I switch on, and the system is calling for heat, the boiler fires up and the pump kicks in.

The radiators begin to heat up.

After about ten minutes, I hear a swishing sound from the boiler, which lasts for about six seconds, and then all hell breaks loose!

A loud hammering, about five or six sharp raps, is heard from the boiler, (which is downstairs in the kitchen).

The noise then migrates upstairs, through the pipes, to the expansion tank area and can be heard hammering and banging it’s way up to the tank itself.

The expansion overflow ejects some water.

The gas in the boiler switches off, (but the pilot remains lit).

The pump cuts out.

The noise stops.

Then the whole process repeats but becomes progressively more frequent.

Any suggestions?

 

[breezer]

i am not a plumber or heating engineer

have you changed / altered ANYTHING recently? and have you tried bleeding the radiators?

 

[tclarke]

i am not a plumber or heating engineer

have you changed / altered ANYTHING recently? and have you tried bleeding the radiators?

Yes tried that. No Airlock!

 

[masona]

Could be your boiler thermostat faulty,try turn it down or blow any dusts around it.Sound like your water is overheating too quickly therefore the only way out is the air vent as your boiler is expanding the water inside the casing.

 

[sifu]

These boilers use two thermostats, one for high one for low. If the boiler o/heats on both high AND low then it is unlikely to be a thermostat problem, although it is possible.
Is the pump definitely running? Sometimes they hum but are not actually moving. Undo the screw on the front (Grundfoss pumps) or loosen the nut on the front (Myson pumps) and check you can turn the impeller manually. A small electricians screwdriver will do for Grundfoss. For myson pull the spindle out as far as possible to engage the impeller and turn by hand. Then turn on the power and visually check it is spinning. If this is ok and you still have problems then the pump impeller has most likely detached, so you'll need a new pump. You can just change the head. Myson do a multi-head that will fit most myson and grundfoss pumps. Try your local plumb center for parts.
The other possibility is that your cold feed is blocked. Check there is water in all upstairs rads and that they can be bled.

HTH, Paul

 

[tclarke]

Could be your boiler thermostat faulty,try turn it down or blow any dusts around it.Sound like your water is overheating too quickly therefore the only way out is the air vent as your boiler is expanding the water inside the casing.

I think I have found the boiler thermostat, on the right hand side at the bottom, about the size of a ten pence piece, with two screws holding it to the chasis.
Is this correct and how do I go about changing it?