Loud Bang After Boiler Switches Off

5hpr

Hello all,

I have recently moved into a seven year old home.  It has a Ideal Logic Code Combi 38 boiler.

In the hall cupboard, there are valves (two) that make a loud noise when the boiler engages.  One of the valves controls heating to the living room and the other, heating to the rest of the house.

I have noticed that when the boiler turns off itself due to meeting the temperature set on the thermostat, there is a very loud bang from upstairs.  It doesn’t come from the boiler or the valves in the hall cupboard.  Any idea on what that could be?  I haven’t been able to identify exactly where it’s coming from but appears to be the 2nd/3rd bedroom (it’s a three bed semi).

Some back story on the boiler, it stopped working a few months ago with a low water pressure warning (L3).  After a reset, it worked again.  I think this was because I was turning the heating off / on with the switch on the boiler and the gas engineer said I may need an “auto bypass” as the valves are shutting and the built up heat has no where to go?  I’m not entirely sure because there is a heater in the hall that can’t be turned off and thought it was the bypass?  Anyway, getting round to working the thermostats I no longer turn the heating off at the boiler and haven’t had a repeat of the L3 warning.  However I’m wondering if this bypass (coming in at £144 to instal) would sort this loud bang?

Sorry to ramble but advice would be appreciated.  I am considering replacing the boiler to something better, but don’t know if it s a waste of money if it’s working.

Many thanks!

Jeepers_Creepers

I'd be very surprised if a 7 year old boiler didn't already have a built-in bypass. Most do. Mind you, it might still struggle to lose excess heat even with this - I guess the by-pass is simply to allow continued water flow if all the rads shut off?

I would phone or email Ideal and ask them for their thoughts before going further. Mention the solution proposed by your plumber.

southcoastrgi

L3 isn't low water pressure it's no flow,
yes the noise is almost certainly that it has no auto bypass fitted,
JC the boiler does have a built in bypass but that's not sufficient if you have two zone valves, 
the boiler is crap but that's not your issue & replacing it won't stop the noise 

Jeepers_Creepers

Cheers, Coastie.

Please keep us updated, 5hpr, and let us know if the by-pass sorts it. Sounds promising.

5hpr

southcoastrgi said:

L3 isn't low water pressure it's no flow,
yes the noise is almost certainly that it has no auto bypass fitted,
JC the boiler does have a built in bypass but that's not sufficient if you have two zone valves, 
the boiler is crap but that's not your issue & replacing it won't stop the noise 

Thank you for your help!  The noise isn’t coming from the zone valves though.  So will an auto bypass still fix the noise you think?  I was quoted £144, do you feel that is reasonable?  Many thanks, you have reassured me slightly as was worried about access to pipes in floor etc.

Apjs87

I get loud bangs after turning the heating off. Not right away though and is either the pipework contracting again or the radiators.