Ideal Isar HE30 boiler not providing CH

[Mikefromlondon]

I am not sure if I am in the right section, my advance apologies if it isn't.


Could anyone shed some light as to why my Mother in law's 5 year old boiler won't provide CH and it is Ok for DHW.

It has no fault codes on the LCD panel, it is showing "d" for DHW and when you open the hot water tap it fires away fine, and the white burner indicator flashes briefly and goes steady and then stops when you have clsoed the tap. The display then reverts to 0 and the fan and the pump stops.

But won't fire CH, checked the room thermostate and the wiring which is fine, checked the thermostate makes the contacts when CH is demanded, the knob on the front is turned to max. And the timer is on a 24hr setting too.

Secondly, I can't seem to find anywhere how Ideal Isar HE30 senses the demand for the DHW.....errrr seems to be no microswitch or flow sensor being used on this boiler to detect when the DHW tap is opned up???

Seems like they are using thermistors to detect the DHW flow sensing, otherwise how would it know when to give DHW priority from the CH mode, my thoughts were that the DHW demand sensor may be stuck in DHW so i wanted to check if this boiler used a diaphgram method or a flow sensor to detect the demand for the DHW, since this demand overrides the CH and so may be why it is stuck in DHW mode and won't run her heating.

I also removed the motorised actuator from the diverter valve and it is the CP type with 3 wires, and it is not faulty or stuck, since when i switch the mains off and On again, it activates (retracts) briefly and then pops out again pushing the pin on the diverter valve.

The Installation manual states that make sure there are no drips from the tap.

I belive the circuit may be overly sensitive that any drips can throw this boiler into permanent DHW mode!!! that sounds like a bad design if the circuit is overly sensitive to go into DHW mode just on a few drips from a leaky or a dripping hot water tap. That surely is not right!

Any help would be welcome on this, and I think one of her hot water mixer taps in her kitchen is a bit leaky or dripping, it is a ceramic 1/4turn taps in her kitchen sink that may be causing it the drips through wear and tear.

But I just want to know how the heck does this boiler sense the demand for a DHW ??? as I can't see anywhere it mentioned on teh circuit diagram or shown anywhere, so what kind of sensing does it deploy??

 

[dcawkwell]

From a quick scan of the manual.
I would say the boiler is looking at the DHW thermistor all the time
to maintain it at a set temperature as I can't see any flow switches
mentioned.

 

[Mikefromlondon]

Thanks a million dcawkwell, that was a very quick respond. yes it is certainly baffling! so i think they must be usining some sort of temperature sensing to determine when the damand for DHW is made, and so it reverts to DHW from the CH, but if it just acts of a very small leaky taps then that can explain why it is electronically stuck in DHW mode.

So I think I will first have to tackle her hot water taps!

Thanks again for your timely reply.

 

[dcawkwell]

Thanks a million dcawkwell, that was a very quick respond. yes it is certainly baffling! so i think they must be usining some sort of temperature sensing to determine when the damand for DHW is made, and so it reverts to DHW from the CH, but if it just acts of a very small leaky taps then that can explain why it is electronically stuck in DHW mode.

So I think I will first have to tackle her hot water taps!

Thanks again for your timely reply.

To confirm switch the cold valve off of the boiler or the stop cock.
Central heating should come back.

 

[Mikefromlondon]

Thanks, I will do that first just to determine the exact cause, shut of cold water supply to the boiler. Indeed a brilliant suggestion, will be going over to hers later this eveneing. Thanks again, you are a gem.
mike

 

[Mikefromlondon]

Right, I have had no luck, the leaky tap isn't the cause, there was a ball valve under the sink and shut it off there, so it stopped leaking altogether, and the CH still did not come on, so there must be another cause. The taps have to leak a fair bit like a tiny stream before it would fire away. ( My estimate is around 0.5l to 1.0l/min flow rate)

Checked all pipe work for leaks, and shut off the water mains as well, only problem was the stopcock would not shut completely and some water was still dribbling from the taps, so I opened fully the cold water tap to release any build up of pressure in the mains, the CH still did not come on.

As there seems to be no visible external flow sensor on the DHW or one showing on the circuit daigram, it must therefore use some other method to detect this, my guess is the DHW temeperature sensor proble, I will have to remove this and see if it is within the spec or may have gone faulty or even covered in muck!

Still have no idea if this will solve the problem, really stuck here now, i also had a look at the condensate trap, and cleaned it all, it wasn't blocked but had some debri, so i also cleaned the sludge in the sump.

All this had made no difference.

On first switching on, the display shows a single bar quickly followed by a figure 5 and then d and then 0, if you open the hot water tap, it goes into d and the white indicator light does not flash but comes on steady indicating the burner has fired, and when hot water tap is closed the light simply extinguishes, and fan continues to overrun for a few more seconds and then stops and the display shows 0 .

Any help would be appreciated.

 

[Mikefromlondon]

I think I might have figured out as to how a DHW flow sensing might work using just a thermistor probe:

I noticed there is a long DHW probe inserted into a tall tube like part, this might be known as a calorifier, and it may have have two chambers to act as a mini heat exchanger where, imagine the outer chamber is filled with primary or CH flow through it, and seperated by a thin heat conducting wall, the inner chamber is through which the cold water flows through when the demand is made for hot water, the probe is dipped into the centre of the inner chamber, such that when the probe is cold, the circuit board senses that the water in the calorifier and the DHW heat exchanger is cold and it fires up the boiler by going into " t" mode...which heats the water in the DHW heat exchanger, via the calorifier and maintains the calorifier and the DHW plate heat exchanger to a heated state.

On page 6 of the manual under sub-heading OPERATION, it says that :
with no demand for CH, the boiler fires only when DHW is drawn off, OR periodically for a few seconds without any demand for DHW, in order to maintain the DHW calorifier in a heated condition" So this is what it would do to keep the DHW heat exchanger heated up all the times, and the round tall body I mentioned above in par 1, call it a calorifier.

So this causes the probe to remain hot, within this calorifier and when its temeprature goes cold, the boiler fires up periodically to maintain its temperature in both the DHW heat exchanger and the calorifier!

So now imagine if a demand is made for the DHW, so now the cold water from the cold water mains starts to flow through the inner chamber of this calorifier and cools the probe down, this in turn now fires the boiler and start to supply hot water from the primary heat exchanger to the DHW heat exchanger, going through the calorifier in which the DHW probe is mounted.

So this probe may have two functions, one it senses when the hot water demand is made, as when the cold water starts to flow through the calorifier, the probe gets cold, and this is sensed by the board and it fires the burner to heat the water in the primary heat exchanger,

secondly it may serve as the temperature sensing probe for regulating the final DHW flow temperature, so this has two functions, regulates the DHW temeperature which is set by a control knob, and secondly as a DHW demand sensor!

when it senses the set temeprature, it stops the burner, and if the hot water demand is still there, this will start cooling this inner chamber of the calorifier and the probe will start cooling off, which in turn continue to fire up the boiler.

Once the hot water tap is closed, the inner chamber will no longer be passing any further cold water, so it will heat up rapidly and the probe will sense the heat and shut the boiler off, and from then on it may periodically maintain this heat within the calorifier and the DHW heat exchanger at the required temperature for an instant supply of hot water when a demand is made.

I think I have a fair idea now where to concentrate, as I can now see how Ideal may have deployed this technique to sense the DHW flow.

So the reason why it is not going into CH mode may be becuause this probe is no longer giving correct readings to the board and the board thinks there is still a DHW demand, and so remains in DHW mode "d" and then 0 instead of going into mode c for CH.

Not sure if this alone can differentiate betwen a CH demand and DHW demand. There could be a fault with the board's logic too, since when the probe is hot, it should be able to go into CH mode when a demand is made for CH, as long as there is no demand for DHW, so it could well be the board or the probe that is faulty. All along I might be totally wrong.

 

[swbjackson]

You're trying to get too complicated. The hot water is controlled by a thermistor which simply holds the water in the water to water heat exchanger at the set temperature. When a temperature drop is detected the boiler fires up in hot water mode to replenish the heat. This is a poor design because although this provides a preheat facility it means the boiler will also fire due to a dripping hot tap and randomly as the heat exchanger loses temperature which can be a nuisance if the boiler is sited in a bedroom.

Back to the CH problem. If the display is showing 0 it is in standby mode with no call for heating or hot water. It's now back to basics time, before you start trying to diagnose boiler faults the first thing to do is check that you're getting a call for heat. You should be getting 240v at pin L2 of the 5 way connection plug. If there is no power here it is an external control fault, if there is power here the fault is internal to the boiler but with no fault codes showing I would be looking at continuity of connecting leads first.

Also make sure that the 5 way plug is fully pushed home, it is possible for the plug to be not quite home and contact L2 not making properly. I had a call out some years ago for no heating and the customer had tied a bag onto the power lead to the boiler to hold old carrier bags. The weight had pulled the plug out slightly.

If a fault was holding the boiler in hot water mode it would have a t or d on the display. The fact that is dropping back to standby makes this highly unlikely.

 

[Mikefromlondon]

You're trying to get too complicated. The hot water is controlled by a thermistor which simply holds the water in the water to water heat exchanger at the set temperature. When a temperature drop is detected the boiler fires up in hot water mode to replenish the heat. This is a poor design because although this provides a preheat facility it means the boiler will also fire due to a dripping hot tap and randomly as the heat exchanger loses temperature which can be a nuisance if the boiler is sited in a bedroom.

Back to the CH problem. If the display is showing 0 it is in standby mode with no call for heating or hot water. It's now back to basics time, before you start trying to diagnose boiler faults the first thing to do is check that you're getting a call for heat. You should be getting 240v at pin L2 of the 5 way connection plug. If there is no power here it is an external control fault, if there is power here the fault is internal to the boiler but with no fault codes showing I would be looking at continuity of connecting leads first.

Also make sure that the 5 way plug is fully pushed home, it is possible for the plug to be not quite home and contact L2 not making properly. I had a call out some years ago for no heating and the customer had tied a bag onto the power lead to the boiler to hold old carrier bags. The weight had pulled the plug out slightly.

If a fault was holding the boiler in hot water mode it would have a t or d on the display. The fact that is dropping back to standby makes this highly unlikely.

Thank you swbjackson for your valuable suggestion, which I agree should be the first port of call, and that is exactly where I started from, I first checked that the room state was getting a voltage across its contacts when the contacts are open and 0v when closed, i.e. when heating is requested by turning up the stat. When you get a voltage across open contacts, this gives you an indication that wiring from the boiler to the room contacts is intact. well kind of.......

However, I now have gutfull feelings that i missed on something here!

I remember seeing something like 26V across the contacts on the room stat, when i had the stat contacts open.....now if the system is running on 230V then the open circuit voltage should be around this 230v !

So may be I missed on the fact it should have been 230V when contacts are open and not 26V which I took for guaranteed was the nominal control voltage as is in some boilers tend to use low voltage for their room controls for added electrical safety.

This voltage at the room stat comes from the boiler via a timer contacts, hence I took it for guaranteed that all was Ok this far.

Oh I am going to kill myself for not really paying attention to the installation manual which clearly states that L2 should be wired to Live 230V via the timer or room stat, or simply bridge L2 with L1 to bypass the external controls.

i am now going to do that and hopefully this is where my problem was.

Thanks again, you indeed shed a light in the right path. I will let you know how I got on.

Still I learned something about Ideal Isar how they use the thermo probe to sense DHW flow sensing. If I had found the wiring problem straight away then may be I would never have stumbled upon this unusual techniqe.

 

[Mikefromlondon]

Managed to sort it out now, I cannot beleive how the 26v across the open contacts in the room thermostate mislead me so badly, i actually assumed it was low voltage driven room stat, like you would get on some boilers. But this 26v was infact stray voltage through either high resistance contacts or capacitive/inductively induced voltage.

If I had read the manual properly, i should have realised that this boiler did not use low voltage but the deadly 230v, hence from the begining I stsrted to stray from faulting the timer control module (BG) and ruled any problems with it, so i started thinking along diverter valve sticking, but it was not, anf also saw the actuator working when mains is briefly disconnected and reconnected, so this lead me to think there may be a problem with the DHW flow sensor that may be continuosly detecting that there is a DHW demand all the time, this is the reason why I probed further into trying to find it used no diaphgram presure differntial micro switch or optical/magneto hall effect type of flow sensor , and this is the first boiler I came across that uses a thermistor to detect DHW demand!

In the end the fault was nothing more than a faulty timer module, physically I took the PCB and found no tell tale sign of tiny surface mounted parts overheating or any parts blown up, it had several smt chips and any one of them could have been the cause. But as I detected 26v I ruled out anything wrong with either the room stat or the timer switch as it also had a 24hr contacts, so that should have bypassed the timer function through its relay contacts.

The problem was even with the timer slide switch being in 24hr, it was presenting a high resistance such that 230v through its contacts was only being seen as 26v at the room state.

we learn from our mistakes and each day you learn something new.

I have now bypassed her timer with a wired link as she said she never used her timer and used the room stat to maintain 18 degrees all around 24hrs at low flow temeprature.

So far so good, I am pleased in the end it was not the boiler, and no expense was incurred except my time I devoted to my mother in law!
#
I fully appreciate everyone's input and thanks again. Mike

 

[swbjackson]

I'm glad it's sorted. At least you've earned some brownie points now.