DHW on Ideal mini c28 - stop start, stop start.

[alexjb1989]

Ideal mini C28

Hi all,

So, I replaced a few parts in the diverter valve things seem to be running a little better on the CH side now.

However, I still get problems with DHW...

- If i set the boiler to hot water only, it fires up ok when water is called for (sometimes it never did this before I fiddled with diverter). And the water gets hot, but then the flame goes out and the led starts blinking fast...... Then after a while the water starts to get warm not hot, then you can here the pump start again the boiler lights and the waters gets hot. The problem is rather than staying on, it keeps cutting out and starting again, nearly like it is cycling????

- A similar problem happens when boiler is set to both CH and DHW. Only before I changed the diverter valve if I called for hot water when the CH was on, it would kill everything once the boiler went out and never start again - now it does seems to start back up after DHW turned off.



Any ideas?

I can post a video if that helps

 

[alexjb1989]

Update...

I have found out that if I put it into DHW mode only and remove the green probe on the left side of the the diverter valve, it will NOT cut out. The led starts flashing like mad, but the water remains hot!

If i leave the probe off the CH has issues, so i have to put it back on.

Any ideas how to fix this?

Something on the circuit board?

i am pointing to the thing i mean in the picture- i believe it as a NTC probe, according to the manual black and blue cables that attach it mean CH Probe - strangely nothing to do with DHW.

 

[ianmcd]

It is indeed a thermistor and the flashing red light is telling you that it has been disconnected and it has a lot to do with the DHW as it tells the boiler what the temperature of the system water is when you are running DHW

 

[alexjb1989]

thanks for your reply.

It doesn't flash red, though. Just the Green LED.

So why does DHW work when set in DHW mode only, and the CH NTC probe removed?

Faulty NTC?

 

[Gasguru]

It might be described as a CH NTC thermistor but it's actually measuring the temperature of the Primary boiler water circuit.
In DHW mode this is the water circulating from the upper primary heat exchanger (the gas to water hex) down to the lower secondary heat exchanger (primary water to domestic secondary water).
In DHW the boiler will sense the DHW temperature using the DHW NTC thermistor but also monitor the primary circuit temperature using the "CH" NTC ie. checking it's not overheating.
In CH mode the boiler will monitor the CH temp using just the CH NTC.
It's up to you how much you want to test the NTC...the trick is to get the boiler to fault, then immediately cut the power and measure the resistance. It's a common fault to find the sensor gets to a particular temperature wherupon it goes open circuit. Occasionally you can find the resistance is way out across all temperatures. Sometimes the act of removing the connector and probing the pins will get the sensor going again. Suck it and see.

 

[nwgs]

I’d be cleaning plate hex and putting 2 new thermistors in.

 

[alexjb1989]

Thanks for both of your replies.

So does that explain why removing CH NTC probe and putting the boiler into DHW mode only allows me to get hot water properly?

Also, as a work around, if I want to run bath for example, is this safe to do so (what I said above)?

 

[shambolic]

The 3 flashing lights will tell you the fault.
It’s in the fault finding in the book.
I’d be changing both thermistors though.

 

[alexjb1989]

Fixed,

Removed Heat Ex and cleaned with Spirit of salt.

Lots of crud came out.

Now filled system with Cleaner, will let that run for a while, then drain down and refill with inhibitor