Kettling Baxi boiler

[franklymdear]

Hello boiler experts. We recently extended out heating system, and have adjusted our Baxi 100/2 HE Plus boiler to cope with the added heat load. This has been done in accordance with the manbufacturers guidance, simply by removing the red jumper on the pcb. However, when the thermostat or timer shuts it down we get boiling on the heat exchanger and bangs in the pipes. Seems to me it needs a pump overrun, but this is not required according to the manual, and as the boiler does not use a permanent live, cannot be simply achieved. Any one else had this problem and solved it?

Thanks

Frankly

 

[namsag]

You can wire in a pump over run have a closer look at instructions

 

[franklymdear]

Not without a permanent live and removing the room thermostat so that the CH is interlocked by the flow switch

 

[namsag]

although it says room stat should not be fitted cant see any reason why it cant be fitted after all its just doing to the heating motorised valve what the cylinder stat is doing to the HW motorised valve
Yep and permenant live is needed how awkward is it to get one to your boiler position.

But phone call to baxi tech will confirm why they don`t want it wired this way

 

[franklymdear]

Thanks for your help, it is much appreciated. Getting a permanent live is no problem, except the boiler does not have a terminal for this. The room stat and the timer effectively cut power to the boiler, hence the pump live switch has nothing to drive the pump with. prpbaly easiest to by a simple off delay timer and wire that to the pump.

Makes it a bit more complicated as this is a twin head, pump plan system. So two pumps and no valve

Cheers

 

[baxpoti]

If you've wired the pump to the P/L connection and have a room stat it's not installed correcttly.

What size flow and returns do you have on a 100,000btus?

 

[franklymdear]

Hi,
No it is not wired to the PL, that is left unconnected. With the Grundfos pump plan, the pumps wire into the wiring centre. The boiler connection is simply S/L, N and Earth. The Grundfos wiring centre has the option to connect with the P/L on the boiler, which would then allow the HW pump to overrun and cool the boiler after the flame is shut down. However, the Baxi boiler is not specified to have a pump overrun, unless the CH system is TRV control only. Apparently the boiler does not need this, as it runs at low temp.

Flow and return are 28 mm, as per Baxi spec

 

[hect]

If its kettling its normally poor circulation down to poss build up of sludge in system.........

Have temp diffs been taken???

 

[franklymdear]

Hi,
Kettling only occurs after the boiler and pumps shut off.

 

[hect]

Well, it could be HEX cooling down??

Poss scale in HEX??