Boiler keeps switching on.

[nedflanders]

Hi, I wonder if anyone can help me with this please.
This is a system with a Baxi Bermuda Back boiler. The heating is pumped, the hot water gravity. There is a room stat and a Drayton Tempus programmer. No tank stat; water temperature controlled by the boiler stat.
The system works okay, except that the boiler keeps switching on for a few minutes, then off again. Not because of a drop in room temperature; the pump doesn't come on. Just the boiler; it seems to just heat itself up, then switch off. It shouldn't do this, should it?
I've tried the boiler stat on different settings but it makes no difference.
Any help would be greatly appreciated as this is not only irritating, but must be wasting a fair amount of gas. Thanks.

 

[baxpoti]

Switch the boiler (hot water time controls?) off

 

[nedflanders]

Hot water controls are off permanently. The water is heated automatically when the heating is on.
I recall that this problem is called 'dry cycling'. Does anybody have any ideas on that subject?

 

[baxpoti]

Which bermuda model is it?

It must be getting a signal to switch on, and then cycle.

Have you got a frost stat on your system?

 

[nedflanders]

Hi. The boiler is a GF3/LFE5 Super. There is no frost stat.
I've been searching the net and from what I can find out, the 'dry cycling' simply reheats the water in the boiler when it falls below the setting of the boiler stat. It's not because the room stat or the hot water are calling for heat.
Apparently wiring an 'interlock' is the answer. Now if I could find out how to do that.......

 

[baxpoti]

Hi. The boiler is a GF3/LFE5 Super. There is no frost stat.

Thats the fire fronts

I've been searching the net and from what I can find out, the 'dry cycling' simply reheats the water in the boiler when it falls below the setting of the boiler stat. It's not because the room stat or the hot water are calling for heat.

Well you learn something everyday

Apparently wiring an 'interlock' is the answer. Now if I could find out how to do that.......

Fitting a room stat and cylinder stat

It must be getting a signal to switch on, and then cycle.

 

[dal5band]

I'd say it is working as designed. The boiler supplies a resevoir of hot water which the room stat and pump take when they need it.

As you do not have a cylinder stat, the room stat can't turn the boiler off because with the boiler off, the hot water would not heat up (if it got used up). You need a cylinder stat and some clever change-over wiring to achieve full controll of the boiler. Then the boiler would go off if both the cylinder stat & the room stat were satisfied.

 

[nedflanders]

some clever change-over wiring to achieve full controll of the boiler. Then the boiler would go off if both the cylinder stat & the room stat were satisfied.

...also known as an interlock....