Boiler not reaching temp

[LeeW32]

Hi all, just moved house. Boiler is a glow worm 25r 4 years old. It's not a combi (ie we have a hot water tank and tanks in the loft...open vented?).

Anyway, with the thermostat turned up (eg something like 24c for my experiment), I've watched the heating water temperature on the front display of the boiler. It just stays on something low (around 42c) for ages...at least 10minutes, and then it suddenly kicks in making more noise (more gas being burnt), and the temp goes up as expected. But then it doesn't quite hit the set temp (which is 68c)...so it gets to 62c in a matter of seconds, and then goes back into 'low gas burning' mode, temp slowly falls back to around 43c....and the cycle starts again.

Rads just get warm obviously.

So doesn't get to full temp, or stay there very long. I'll book an engineer, but I'm interested to know what others think?



Thanks!

 

[The Artfull Bodger]

So your boiler goes from 43 to 62 c in seconds? Could be see a circulation issue, rads not open, pump not working as expected, system filter clogged, heat exchanger clogged. Expect your getting some circulation as boiler is not reaching stupid temps and banging. It could be other stuff as well like thermistor or pcb, difficult to diagnose without being there tbh.
Is it not still under warranty with Glo worm, I assume you have it serviced yearly, you might be lucky. Get someone round to make sure it's a boiler issue and then get them out if it is.
Edit- does your hot water cylinder get up to temp ok, or Is that affected too?

 

[LeeW32]

Hi...thanks for response. Sorry, shouldn't have said seconds...it's not that quick...more what I would expect, a degree every few seconds (so maybe a minute or so).

Sadly the previous owners didn't have the boiler serviced...apart from when we asked them as part of the sale...which didn't report any issues so I had (wrongly) assumed it would be ok.

Appreciate it could be any number of things so will get someone in...just wanted to see if it was something typical, or something I could try to diagnose myself.

Thanks

 

[RJC]

Have you found your hot water being too hot as it could be the 3 way valve is stuck so its heating your rads as well as hot water.