Britony Combi 80 (central heating running when off)

[nigelb1]

My CH system is running even when the CH side is switched off.

The electronic programme unit is in the off position and the OFF/HW/CH selector switch on front LHS of the boiler is in the HW only position.

However the boiler pump appears to be running all the time and the burner is firing for 6 sec every 30 sec.

The only way to stop it is to remove the mains power or to select off.

Conversely when CH is switched on this ignition cycle continues and the radiators do not get warm.

Has anyone come across this fault,any ideas?

Thanks.

 

[kevplumb]

first thought dhw flow stitch stuck

 

[nigelb1]

OK thanks, I have downloaded the GA for the boiler and BOM.

Is the DHW flow switch also referred to as the Water Throttle?

If so there are two identical flow (throttle) switches, looking at the hydraulic block from the front is the DHW throttle on the LHS?

I assume its full of crud, can I clean or should I just replace, if so do I ned to just isolate the mains water or do I need to drain the CH system as well. Should I replace both if one has gone, just in case?

Thanks Nigel.

 

[kevplumb]

its the one on the right according to the bumph ive got

witch tbf is carp

you will only need to turn the water off and drain it open a tap

the pin sticks in the sleeve inside the switch

wheres agile when you need him

 

[Gasguru]

Fault probably due to the water throttle reed switch tines becoming magnetised over time. Unclip the wiring harness and see if it stops firing. Heating will often appear to be on due to diverter valve let by (another common fault) to the heating circuit. The replacement reed switch assembly has been re-designed (not cheap either).

 

[nigelb1]

The mains water enters the boiler via a shut off valve and into the base of the LHS Throttle Assy. I had therefore assumed that this was controlling the DHW side. Is this incorrect?

Anyway here are the results...

If I disconnect the RHS sensor and select HW only the pump doesn't run and the boiler doesn't ignite (as before), when opening a hot water tap the boiler doesn't ignite. If I select CH the pump runs but the boiler doesn't ignite and no hot water.

If I disconnect the LHS sensor and select HW the pump remains off, boiler does not ignite and no HW available. But when I select CH the boiler ignites and the radiators get warm, the CH system appears to be running normally.

If I am able to get the CH system to work in one mode and the HW in another, and no HW comes out in the CH mode, I assume that the Three Way Valve is working and not stuck?

Does this imply that the LHS throttle switch needs replacing or both?

Are there any additional test I can try?

 

[Gasguru]

The LHS sensor is for DHW....you will find with the harness disconnected and the hot tap off the resistance will be near zero indicating a faulty reed switch.

 

[Agile]

It could be that you disconnected the DHW flow switch when the boiler was hot.

Selecting CH at this time might have been with the boiler thinking it was hot enough.

I suggest you depower the boiler or just leave it for 1/2 hour with the DHW switch disconnected to cool down before you tried CH.

If you turn off CW supply to boiler, open hot tap and then unscrew the DHW flow switch you may find its dirty and the magnetic float has stuck. If not then the reed switch has become magnetised and stuck on.

Tony

 

[nigelb1]

Well many thanks for all the help over the weekend.

Based upon the above I have ordered two new throttle switches tonight (£33), should arrive 3-5 days. In the meantime I will leave the boiler switched off overnight and when not in use.

Will check the resistance and drain, clean and replace the throttle switches on Friday, assuming the parts have arrived.

Thanks will keep you posted on the outcome.

Nigel.

 

[nigelb1]

Thanks to kevplumb and gasguru for this solution, replaced both throttle valves, boiler and CH working perfectly.

Regards Nigel.