Glow worm hot water problem

[siddiq]

Hi,

I have glow worm 100e combi boiler which keeps going off on off on when hot water is turned on. Central heating is ok. So far I have swapped out the main pcb and hot water thermistor, but problem still persists.

I would appreciate any ideas, assistance.

Siddiq

 

[boxster]

check valve pressures and maybe change the hot water micro switch, if the hot water is running hot cold hot cold - diaphram ect...

if the boiler is actually going on off on off try gas valve pressures and there must be a problem with the micro or the arm

 

[siddiq]

Hi,

Thanks for speedy reply.

The boiler actually does go off and on and off.. when the hot water is turned on. When central heating is on the boiler stays on.

I will check the switch tomorrow.

 

[boxster]

again that sounds pressure related, check for correct incomming and check the burner pressure. also go to your boiler, remove the case get a friend to turn the hot water tap on, look for the h/w micro switch, its the one the arm lever moves. once you have found it , tuen the hot water tap off. press the micro switch in and hold it, if your boiler stays on, replace the micro switch, realy easy 2 min job, no drain down.

 

[ChrisR]

What frequency of on/off?

Could be scaled up primary (or secondary if you're in a hard water area) side of ther tap hot water heat exchanger. Won't transfer enough heat so the boiler turns off, then it cools, etc. Could be faulty sensor or pcb if it isn't modulating (turning down gracefully).
Both are easy to check - temp drop across the h/e should be 11ºC usually (check with GW), check volts on gas valve mod coil - should vary as things warm up if tap is half on..
Also what is your hw flow rate in litres per minute at showering (from hw tap alone) temperature?