hot water cutting out! performa 28

[berthollywood]

rubber felt a bit loose but was not damaged in anyway,the differential valve is still operating the pressure microswitch in the normal way,and is still operating microswitch up-until hot water cuts out,if the diaphram was damaged would the micro-swith not be operated?

CH working normal,the CH return stop-tap was closed preventing the heating from running,must of been closed by plumber last week.....

ive ran the CH for about 30 min to see if it was cutting out too but didnt,gas was modulating as it should,so still left with same problem of hot water cutting out

[CharterGAS]

is this the performs 28 i??
re diaphragm - if the rubber is any way deteriorated no mater how minor it could be enough to fluctuate the pin which hits the micro switch there may even be a tiny hole on it!!

my best bet would be to change the hot water ntc and then see how you go. then maybe think about replacement diaphragm if you don't want to get an engineer out.

[gascob]

I'm pretty sure you have a partially blocked plate heat exchanger on your performa, if it was a problem with the diaphragm i don't think you would have the on/off problems you are having.. it sounds like the restriction is causing the boiler to reach temperature before it has had chance to transfer the heat to the tap water.. also make sure the low gas pressure is set correctly...

[berthollywood]

can i strip the plate heat exchanger down and clean it or will it need replacing?also the central heating is running fine so does that cancel low gas pressure out?

[gascob]

you can take the plate heat exchanger out and give it a good rinse out through a tap whilst giving it a bit of a crack with some grips or a screwdriver, you should see some chunks of debris coming out.. if you live in a hard water area it could be scaled up which you will struggle to get out(i do know people who have soaked a plate in calgon overnight though) they are easy to take out on a performa but make sure the 4 washers are intact before you put it back together or it will be leak city.... i suspect the low gas will be ok with the ch being fine...

[berthollywood]

do i need to drain off the central heating to remove the heat exchange or just the hot water?

[gascob]

you will need to drain both the heating and the hotwater...

[spacethegas]

i think gasgob is pretty much there.
the primary side of the dhw heat exchanger/calorifier is full of crab.
pull it out descale/desludge it.
was the boiler fitted to an existing system ?
was it flushed treated with chemicals when installed ?
if no or you dont know to either q the system should be powerflushed & treated cause it will happen again.

[berthollywood]

The boiler and central heating system is about 4 years old,all radiators and pipework were new at the time they were installed

is it ok to take it out and use household descaller,or will this damage it?

i think there was fernox put into the system when it was installed,whats the best product to add to my system?

[gascob]

take a water sample from the bottom of one of your radiators, a good litre will give a good indication of the water quality, i have seen new builds blocked after 3 years due to incorrect commisioning. i would use a product by sentinel or fernox to descale the heat exchanger, go on their websites and have a look at their products as they do a few different ones......