Ideal istor thud/case vibration when turning off

[ecswtrav]

Hello all,

I know the boiler doesn't have the best reputation but its generally worked well over the last 5 years or so. Having said that, I've recently noticed the boiler is making a thud and the case vibrates. The boiler is on a service plan until tomorrow with Homeserve and the chap that has been out has replaced the ignition electrode and a few other related parts thinking it was an explosive ignition.
Turns out its not an explosive ignition but although he has pinpointed what's causing the noise he is unable to repair it but says it's not a problem to the boiler or us!
There is a 2 port (i think) zone valve in the boiler that he was showing me. The lever on the top, once it clicks to the 'off' position (or he pulls it over to the 'off' position) causes a thud and the case vibrates for a second or two. The boiler fires up fine, with no noticeable noise but makes this loud thud whenever this valve switches to the 'off' position. The chap tells me replacing the valve is not the problem as it works fine.
Just wondered if anyone knew what this could be and whether it is, as the chap says, perfectly safe?

Thanks a lot

 

[garygvl]

Sounds like cylinder coil vibrating when hot water demand ends and motorised valve closing with pump still on overrun. You used to be able to get what they called a judder kit which stopped the pump while the motorised valve was moving. Don't know if you can still get them but its safe as per Homeserve if this is the problem

 

[ecswtrav]

Thanks so much for the reply. I've decided for the time being to live with it but you've got the nail on the head with it being the cylinder coil. I've had the boiler cover off and that's exactly where the noise comes from. In the meantime I'll keep an eye out for mine of these kits. I'm assuming it's not a kit specific to the boiler? Maybe something will come up on eBay? But thanks for the advice