(unspecified) boiler bangs at start up

[allone]

Hello all,
A few minutes after a cold start my CH system makes noises like a wounded donkey trying to kick it's way out of the boiler cupboard. This only lasts 3-4 minutes and then the system operates fine until the next cold start. The noise centres around the air seperator about 12" from the boiler, it shakes the cold feed and air escape pipes.
For those who like a more technical description the noises are groaning/shuddering/clanking all at the same time.
Hopefully someone can point me in the right direction, thanks for reading.

 

[slapper]

I seen one of those on Skeggy Beach

 

[allone]

I seen one of those on Skeggy Beach

Well, that's where they belong!
Any ideas to get rid of mine?

 

[allone]

Can anyone help with a serious answer please?

 

[Dan Robinson]

If you want a serious answer then you will need to post some serious information about the system,

Until then we will just take the pish.

 

[allone]

If you want a serious answer then you will need to post some serious information about the system,

Until then we will just take the pish.

OK, here goes then.

20yr old Gloworm fuelsaver,
Open vented system,
Myson aerjec air seperator,
F&E tank in loft,
10 single rads with TRVs on 8mm microbore.
Grundfoss variable pump,
Danfoss programmable roomstat,
Horstman CH/HW control.
HW cylinder below boiler.

The noises only happen on cold start, after 4-5 mins it settles down and runs smoothly until the next cold start.
Noises appear to be centred around the air seperator, but hard to be sure as it's close to the boiler.
Some days it starts up with no noises whatever, then next time they are horrendous, can be heard by neighbours.
Sometimes on start with HW off, noises can be stopped by using boost HW button on control box, other time even with HW & CH on it starts with the noises.
I am keen to keep the boiler in spite of it's age, I am aware that many recommend a new boiler but want to avoid the disruption of a change if at all possible.

 

[allone]

Anyone please?

 

[picasso]

sounds like the pump isint starting on the call for heat, sticking pump, faulty overrun stat? you really need someone to look at it.

 

[Danoil]

I seen one of those on Skeggy Beach

Eeoor, eeoor, 'e always goes down there

 

[allone]

sounds like the pump isint starting on the call for heat, sticking pump, faulty overrun stat? you really need someone to look at it.

Many thanks for your answer.
Pump checked and running OK. Is the pump really likely to be at fault? The system runs OK after a few mins. Plus it's fine on warm/hot starts. The noises only ever happen when everything is cold.
Thanks again.

 

[allone]

sounds like the pump isint starting on the call for heat, sticking pump, faulty overrun stat? you really need someone to look at it.

Many thanks for your answer.
Pump checked and running OK. Is the pump really likely to be at fault? The system runs OK after a few mins. Plus it's fine on warm/hot starts. The noises only ever happen when everything is cold.
Thanks again.

Any other suggestions please?

 

[Gasguru]

For testing purposes you could wire the pump feed onto the boiler permanent live feed to rule out boiler pump overun thermostat issues. See if it makes a difference.