Worcester 28i RSF Boiler Overheat cut-off thermostat problem

[Stonedofmoo]

Morning all

I have a Worcester 28i RSF Boiler which has been in place and operating since 2003. It has a overheat cut-off thermostat which when trips, turns off the gas so you don't get hot water.

This has now tripped twice in the past 24 hours, whereas before then it has never tripped at all.

Now I just wanted to check this with you guys because at the moment the radiators are all drained of water while we redecorate the front room (I had to take the radiator off the wall).
Would this affect the boilers ability to produce hot water? I didn't think so as I have been in this position before without any water in the system, and the switch never tripped then when we were using hot water.

3 questions then

1) Can the hot water work correctly and independently without the radiator system being full of water?

2) If the switch is tripping, what could be wrong with it. Is it worth me calling in a service engineer? I can reset it, but I doubt it should be tripping.

3) Slightly unrelated, but this boiler is now 7 years old. I know boilers get more efficient all the time, but at what point should I consider replacing it for a more modern appliance. I notice the new Worcester 28i Boiler claims to be 30% more efficient thanks to reusing the exhaust gases.

Any help appreciated

Chris

 

[jimstreet]

yes if the heating system is completely empty it will affect it because when you have the hot tap running obviously the boiler fires and heat the water, but when you turn the tap off, the heat is stuck in the heat exchanger and needs somewhere to go, and the pump will kick in and generally would have a bypass in the system to dissapitate the heat, so the boiler will overheat if this has nowhere to go, had a simialar problem like this a few weeks ago on a job!

 

[bengasman]

Not sure if the old model i-series are ok to use without rads. MI will tell you.
Pressure gauge will still need to be between 0.5 and 1.5 at all times.
No point replacing with new i-series just to get a bit more economical; no chance at 30% saving.
The i-series have always been a budget model and decidedly less good than the cdi.
To get a new cdi properly installed will cost you at least 2 grand, it will take a lot of gas savings to make up for that.

 

[Stonedofmoo]

What is the difference between the CDI and I series boilers then?

I've refilled the system and so far all seems well. As it's been many years since it was installed, should I get it 'serviced' at all? Or is that really a waste of money?

 

[bengasman]

difference between i and cdi is like mercedes a series and s series, no comparison.
annual service including inhibitor check/topup can double the life expectancy of a boiler.
More boilers die from neglect than from old age.

 

[Stonedofmoo]

Ah interesting, cheers for that tip. Should I use an inhibitor when I refill the system? I so reguarly take radiators off the wall the water practically comes out clean, but I often wonder if I should put something in there to be sure

 

[steved101]

combi boiler needs water in the main (primary) heat exchanger to be able to heat the hot water (diverter vale diverts it to h/w heat exchanger when a tap is opened - so if the system is fully drained - then the boiler will overheat/not fire/go to lockout as no water is inside it!!!

 

[bengasman]

Old model i-series is a bi-flow Steve, but I think the pump kicks in for an overrun after dhw anyway. Besides, upon contemplation I think OP took the radiators of one by one, in which case defo water needed at proper pressure.

To OP, by the sound of things, your boiler is way overdue for a service anyway, so I recommend you get a good local RGI in as soon as all the rads are back on the wall and ready to stay there; the sooner the better.