Ideal Logic Heat 12 boiler fault

[flexyboy]

Y plan System description

Ideal Logic Heat 12 (heat only) Type 41-399-99 s/n XV20583700014230
Drayton LP722 2 channel timer/prog
Drayton mid position valve
Corgi room stat
Iflo 3 terminal cylinder stat
Danfoss circ pump

All the external components have been individually checked and tested and all are working to specification

All Wiring via the central connection center (junction box), has been checked to Ideal installation spec and individual component spec and is correct and in good condition

Fault

Call for CH only- display changes from 0 to c (with room stat not satisfied)

It is approx 10 seconds from CH call on programmer before boiler display changes from 0 to c, indicating the mid valve position has moved to appropriate position and has sent out the switched Live – orange to the boiler SL terminal

The boiler burner indicator lights for a couple of seconds then goes out and stays out


Switch on call for DHW, boiler lights and stays lit, flow water heats and sends hot water to cylinder AND rads OK

When HW cylinder stat is satisfied, boiler blue light extinguishes but display still reads c (because of call from CH side- room stat NOT satisfied)


In summary boiler will not operate DESPITE there being a call for heat (as indication on display panel) UNLESS there is a call for DHW simultaneously

The condensate drain is clear, and the internal trap is clear and full


Question

Why, when there is a call for CH only (display changes from 0 to c) does the boiler NOT stay lit, but will if there is a simultaneous call for DHW – indicating that the internal flow sensor ( and circ pump OK) , flow and return thermistors ok, and clearly the fan and ignition circuits are OK..

Surely when there is a c on display the boiler should fire up and it does NOT differentiate whether that is a DHW or CH only call, the control of DHW and CH is mainly controlled by the external components e.g. thermostats

Any thoughts would be much appreciated

Thanks

 

[dilalio]

No circulation round CH circuit?
Any isolators that have been closed?
Pump pushing?
Detect for flow would be part of my fault finding.

 

[flexyboy]

dilaio. Thanks but as stated flow is fine around CH circuit, pump switches on as soon as call for CH

 

[Madrab]

dilaio. Thanks but as stated flow is fine around CH circuit, pump switches on as soon as call for CH

Don't see where you said the flow was OK in CH mode, you mentioned the external components have been checked as ok but not that the pump is actually running and there is flow through the boiler in CH mode?

As @dilalio suggests, that behaviour is typical of the boiler firing up but with no flow, the flow sensor shuts it down very quickly. If it's running ok in HW mode then there is flow. In CH mode, as it fires up ok then really the only thing that would shut it down that quickly would be a no flow situation. if it was anything else then it would do it in HW mode too.

Where is the pump wired from? It should really be direct from the boiler, is it via the wiring centre and 3 port? The HW doesn't send a SL from the 3 port but the CH does.

 

[flexyboy]

Thanks for reply.
Pump is from boiler
When just CH selected, pump switches on and is circulating, with 0 changing to c after about 10s. At the same time c appears SL goes to 240v. Blue light comes on for a few secs , then off.
If then HW selected, then boiler lights, pumps stays on, and flow heats and gets split at mid pos valve to send hot water to rads and cylinder

 

[Madrab]

OK, As suggested, the boiler's dumb when it comes to what is selected as that is external to it. It gets a call for heat, it goes through it's start up routine and then runs. The only thing that would stop that cycle internal to the boiler is a fault in that sequence, once it's lit then the only other thing that stops it is an overheat condition or a no flow condition.

If the HW calls and everything runs then that would usually rule out the boiler. The only other separation in a Y plan is that the HW sends it's SL through the programmer> Cyl Stat > boiler, whereas the CH only call or both comes from the 3 port (depending on what's satisfied).

Does the SL drop out or stay @ 240v? I'd suggest, everything else being equal, that it has to be dropping out being the only other thing that would turn off the run light and shut the boiler down, if so then it's time to look at the 3 port behaviour/wiring.

 

[flexyboy]

Hi. Perfect info
SL stays at 240, also confirmed by c on boiler even though burner will not light.
I have checked 3 port, orange only live when both grey and white live. Confirmed this out of cct, by checking continuity and manually moving valve

 

[Madrab]

SL stays at 240, also confirmed by c on boiler even though burner will not light.

OK, If the SL @ the boiler stays a 240V and the display stays at C then we're back to a no flow situation. It's the only other fault that would cause the boiler to shut down at that point. The boiler is still getting the call (SL) but the boiler flow sensor says there's no flow and stops it firing. That brings us back to the 3 port.

What make is the 3 port. May be an idea to take the head off and manually try the valve and see if you can prove the valve has moved over properly closing the HW and opening the CH port.

 

[flexyboy]

It's a corgi,
Yes taken off control head. Valve moving fine as is control head and providing correct switched SL output on orange dependent on motor position.
Confusing

 

[dilalio]

once it's lit then the only other thing that stops it is an overheat condition or a no flow condition.

This ^^^

 

[dilalio]

Lazy pump.
Can't overcome CH resistance but gets it round cylinder coil.

 

[dilalio]

KISS!

works for DHW
Doesn't work for CH

Start from there.

 

[snb1]

think you have forgotten the HW off wire connection in the wiring for a y plan. that why it works with the hw demand on until the water reaches temp. check that you have 230v on the grey wire when there is no demand for hot water but heating is demanding.

I have attached a copy of the Honeywell wiring control systems. it has a very good fault finding section.

 

[flexyboy]

Hi. Tks for that.
The HW off 240v from timer is connected to grey mid pos valve and has 240v when no HW demand

 

[dilalio]

Put HW on and "manually" move valve to CH (maybe with head off).