Baxi 105e - H/W cycling on/off

[bewsh]

Alright guys?

Got the above boiler giving a bit of grief. The hot water cycles on and off as the boiler gets too hot.

I changed the diverter valve after one of my work mates but the problem is the same.

I changed both thermistors as well.

Plate heat exchanger was replaced 12 months ago and a magnaclean was fitted at the same time.

The internal bypass gets red hot - baxi tech say this only gets hot if there's a blockage somewhere, so I have taken the plate heat exchanger off to see if there's any muck coming out of it, but it's nice and clean.

Have any of you guys got any idea what could be causing this?

Oh ye, heating works fine.

 

[Soulman]

Although you have replaced the thermistors, you could have a duff one on the DHW. Have you checked the resistance? Should get about 12-13,000 ohms when cold. Other than that, i can only think of a pcb fault, as you've pretty much covered everything else.

 

[bewsh]

Ye, checked the thermistors, they were all good.

Can't imagine it being a PCB fault as the bypass is getting red hot - and baxi tech say that'll only happen if there's a restriction somewhere, but can't think where else it can be as the heating is all working fine.

Does anyone know if there are any filters on the hot water circuit? I know there's one on the return iso, but that wouldn't affect the dhw

 

[dave1]

When you take the plate heat ex off, check inside the hydronic for crud too.