Potterton Netaheat Profile – blocked air hose restrictor
About a month ago (in June 2022) I drove down to Portsmouth to fix a Netaheat Profile which had stopped working. A straightforward repair or so it seemed both on the phone when discussing the fault, and also when I got there. The little air restrictor in one of the two hoses connecting onto the air pressure switch was blocked and all I needed to do to get the boiler working again was poke the dust out of the (very tiny) hole, using the piece of guitar high ‘E’ string I carry specifically for this purpose. (It’s a VERY common fault on this boiler, and on all Netaheats actually.) So as expected, I reconnected the hose to the air pressure switch and the boiler lit beautifully. All sorted out or so I thought. I carried out the four statutory safety checks, billed the customer and left. A routine repair, not particularly noteworthy in any way.
UNTIL… a month later when the customer texted to say the problem had returned! Most unusual, a guarantee call-back. So I drove back to Portsmouth and gained access to the air pressure switch again to find out what was going on.
I pulled the air hoses off and found the air pressure switch and the hoses full of water. This would explain the failure, but WHERE did the water come from? There shouldn’t be any inside air hoses! I checked the air hose connections at the top of the boiler where they join the flue – all appeared well. The flue itself was in good order and there had been no rain for weeks so rain ingress seemed unlikely. Then I figured it out.
On checking the integrity of the diaphragm in the air pressure switch by blowing gently into one of the hose connections, I found air would pass straight through the air pressure switch and out of the other hose connection, which it most definitely should not. The diaphragm had ruptured, allowing flue gas to pass done the air hose and straight through the air pressure switch. Flue gas comprises approximately 50% water vapour so as the flue gas cools in the air hose, the water vapour condenses out inside the hose and inside the air pressure switch.
So I fitted a new air pressure switch with a diaphragm is good condition which will not allow flue gas to pass through, and the boiler is back in full working condition.
Whether the ruptured diaphragm had been present on the first visit and I hadn’t noticed, or whether it happened in the three weeks after my initial repair is impossible to know, but given the doubt I did not charge to the customer for the new air pressure switch or for the second visit. I treated it as a call-back under guarantee
Lots more about the Netaheat Profile on my Netaheat Repairs website, here:
netaheat-repairs.co.uk