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Discuss Logic Code Combi (issue?) in the Central Heating Forum area at PlumbersForums.net

Hi all

First timer here - after reading a lot of the advice present I thought it would make sense to get stuck in and throw something into the ring.
I am a Landlord and Agent operating new build properties in the Nottinghamshire areas, and have what seems to be an ongoing problem with one specific property.

The boiler fitted is a Logic Code Combo ESP1 38, room stats are Danfoss TP5000si 5/2, zone valves are Danfoss HPV2 (the house also has usual TRVs etc.) - nothing much else to these new builds. The CH and hot water both work at all times when called upon, including CH when timers are called and also when operated manually. There is no pre-heat function on this boiler.

The tenant got in touch explaining the boiler was firing up, mainly in the morning and the evenings, and the room stats were not calling for heat (downstairs set at 21 degrees, upstairs at 18 degrees). The boiler display was showing '00', standby mode, and no other fault codes have been showing. The radiators would get slightly hot right at the top, and the auto bypass system would get hot.

Installing plumber/electricians attended and couldn't find any faults, however suggested I get an Ideal engineer to attend and inspect.
  • Ideal engineer found a 84v backed to the boiler which he assumed was from a faulty zone valve, installers re-attended and couldn't find any fault with the zone valves.
  • Heating engineer attended and couldn't find any fault, suggesting I request Ideal engineer revisit and attempt to coordinate a visit with the installers
  • In the meantime I have zone valves replaced with brand new ones in case there is an intermittent fault with these (made no difference)
  • Ideal engineer attended and demonstrated 80-90v back feed on the cable running between the boiler and the wiring centre upstairs
  • Electrical installers isolated a single cable with 'phantom voltage' and fitted necessary resistors to reduce the standby voltage which was understood to be causing the boiler to fire up intermittently (please note this 'phantom voltage' didn't show when the Ideal engineer first attended, it was unexplainable).
  • Electricians sign off the property having inspected all the components and operability, the installing plumbers also sign it off on the basis that all is working correctly and what the tenant is hearing is simply the boiler pump running to maintain a flow of water through the heat exchanger and also dissipate heat in the system (tenant explained that he could hear water flowing through the bypass system).
  • Tenant explains the 'problem' is still persisting and so I call out my heating engineer to inspect again; he struggles to find a fault but suggests I get Ideal to return and install a new PCB as he knows these can sometimes be faulty
  • Ideal engineer attends, installs a new PCB and cleans the diverter valve of some debris which he believes is allowing some water into the CH system. He also inspects the boiler and is satisfied that all is working as normal and as intended.
  • Tenant explains that a problem continues to persist.

If anyone might be able to shed some light on this that would be great, my instinct now is that the boiler is working as intended but I thought I would float this on here for some combined input in case anyone might shed some light. The system has been investigated extensively and save getting a new boiler fitted, all the parts that are likely to be causing a fault (even if there is not one showing) have been replaced for new, inspected and re tested.

Thanks, and Merry Christmas all
This is pretty simple boiler - if it is firing unexpectedly - it is being switched either by a frost stat (if fitted), Danfoss controller via a zone valve or a dhw demand.

The boiler will not fire from any of the above inputs with the display showing 00 - standby. So you need to establish whether or not that is indeed the case.

I would bridge the thermostat / timer input at the boiler and thoroughly check out the boiler performance / operation. Operate the system with the zone valves open on the boiler thermostat.

Establish if the controller is wired for 240 or 24v control. The connections are different.

Establish the operating mode the controller has been programmed to - normal, optimum or delayed start. If in any doubt perform a factory reset of the Danfoss Controller.

Thereafter, bell out all the wiring on the spur and the control circuit - for both continuity and correct installation - the fact that you have had a stray voltage at the boiler does not bode well that the control system has been wired correctly.
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I would personally also get heating engineer to make sure, if all else is satisfactory, that no electrical links have been left in anywhere.

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