Gloworm 30cxi Boiler Short Cycling

richardc1983

Hoping someone can help. This boiler is really starting to annoy me now thankfully I have insurance on it but the engineers who come out have sometimes been clueless.

Over the last few years it's had main Pcb replaced, new heat exchanger, fan unit and various other things. The last repair was a month ago and was the main pcb that had blown. Now we have started to use the heating because it's got colder I've noticed the radiators take ages to get hot and then when they do they go cool for a while and the burner doesn't come back in for a while.

When it does kick back in the display shows the flow temperature going up very quickly (it's set at about 50c sometimes lower) and then the flow temp can hover at like 51c then you'll see it drop to 48c then back upto 52c and will jump up and down like that and then the burner cycles off.

It never used to do this the boiler burner could be on for about half an hour sometimes longer just ticking away modulated down low. All the radiators are fully on in the house so there should be plenty of flow. I've tried turning the flow temp up but it does the same pretty much.

When the burner is off the flow temp quickly starts dropping and then the fluttering of temp on the display occurs it will flicker between 42-38c then backup 40 then may go back down to 38 before going back upto 41c. When it used to work ok sometimes it did cycle quickly because we run the flow temp quite low anyway as low as 45c sometimes but the house was always toasty can't get the rads more than Luke warm at present. The temp on the display I am assuming is the boiler flow temp? The return pipe is luke warm whereas the flow pipe is hot.

I'm pretty sure there is no blockage it was all drained down the other year to replace the trv's in the house and inhibitor fitted. The heat exchanger was replaced after this though as it was blocked about a year ago.

Even when I reset the boiler at the power switch it is doing this thing where the fan surges - like a car revving when I turn the power off with a f12 fault code. It really doesn't seem well at all. Turning on the hot water seems to clear it but it does this for about 5 minutes before sorting itself. I have checked all PCB connections and they are all fine. During this time the pressure digits are going up and down like a yo yo.

What could possibly wrong with it - other than it being a rubbish boiler!

Thank you.

sk240

Have all of the radiators been ballanced correctly, so that they are sending cold water back to the boiler?
If the circuit is fully open, and the flow and return is at the same temperature, then the boiler is short cycling because the water is already hot.
Ideally you need a 15 degree difference between flow and return.
If its still no good, then it might be that the boiler is just over sized for your application (how many radiators and of what size is it feeding?)

Andy_WSM

Bit late to the party on this one...

Could it be that the circulating pump[ is faulty and not pushing the water around the system quickly enough? If the flow pipe is red hot and the return pipe only luke warm, this could be the reason?

If you can find how to get into the service menu for the boiler (you'll find details online) then you can adjust the amount of time the boiler stays off for between cycles which may help in the mean time.