Greenstar Heatslave Oil Boiler Overheating and Pump Running 24/7

[Johntheo5]

You're correct, yes, A (DHW) is default and you moved the diverter manually to B (CH), but is the boiler still looking at the store temperature (for one reason or another) which is now not getting any heat due to the diverter being forced to CH? so maybe the boiler just keeps firing away merrily until the Hi Limit stat operates, or something like that.
Can you fire the boiler manually on DHW (don't force the diverter) and see what happens? but ensure you have a hot tap open to flow say 5.0LPM which will require a boiler output of ~ 12/13kW at 55C. What is the boiler output?.

You are saying that if you try to put the CH or DHW on "normally" as per the instructions above, that nothing happens?, but it will if you press the hi limit reset??, try that again, press every reset in sight!!.

 

[scottwhittaker]

If I don't lock the diverter to CH then the boiler heats its water tank which is default behaviour when the tank isnt up to temp. So I believe the tank thermostat must be working?

Regardless of if its on CH or DHW, after running for 10 mins say, the dials on the front should cut the boiler out if I turn them right down but they just click and the boiler keeps heating whichever water it's set to.

I can't actually put the CH on "normally" ie turning the external thermostat up, as firstly I'd have to turn the boiler on at the spur and secondly the boiler will always heat the water tank first but this is heated so much it trips the high level stat. Yet, it must only know the tank needs heating from the tank thermostat data.

I'll try the DHW trial but I'd expect it not to trip the high level stat as I'll be withdrawing water constantly.

 

[Johntheo5]

Isn't there someway of switching off that DHW preheat so that the boiler won't fire on DHW until the (if) a flowswitch detects a DHW demand?. IF you don't have the DHW programmed ON will that prevent preheat and the boiler just run in CH mode?.

 

[scottwhittaker]

No its actually called the Heatslave Tank and cannot be switched off or bypassed. I've run it with a hot tap open and it just gives hot water as normal and keeps running. I turned the hot water dial down and it clicked but the boiler kept firing/running. The pressure didnt rise much either.

 

[scottwhittaker]

Ok done a bit more testing.

All the relays on the PCB are operating, none are fused open/closed. I think one is the burner relay which clicks on fine when the power is supplied to the boiler. The middle two are the DHW and CH relays and when the dials are turned up down (or the appropriate water reaches the set temperature), they open close as well, this is also the clicking noises mentioned earlier. The other relay is some sort of fan/post purge/safety relay and this also operates as the boiler fires up.

Still no closer to figuring out why the boiler doesn't stop firing at the desired/set temperate.

 

[Johntheo5]

What is the Boiler Output?.
You said the Boiler continues firing as per normal and keeps running, if you just run a trickle of HW, say 2.0LPM, then the power required assuming a 65C HW temp from a present mains temp of 17.8C and a boiler efficiency of say 78% is only 8.5kW and 12.7kW at a HW flowrate of 3.0LPM, if the boiler output is higher than this in either case then it should still trip out on the HL stat, if not, it should cycle occasionally.

 

[scottwhittaker]

The boiler has not displays with data or anything but the hot water was fine for the 10 minutes I ran it for.

 

[Johntheo5]

You won't know what the burner jetting is but the boiler model should be at least displayed, 12-18 or a 18-25??

 

[scottwhittaker]

Its an 18/25 model

 

[Johntheo5]

OK then, its more than likely jetted to 25kW (Combi) but even if jetted its minimum of 18kW it requires a flowrate of 4.2LPM to absorb that power under the above conditions, you might measure the HW flowrate with a container, reduce it to ~2.0LPM, it simply can't keep running then if the HL trip is operating at 100C as it will take a flowrate of 2.4LPM to absorb even 18.0kW at a HW temp of 100C.

 

[scottwhittaker]

Is this to test the HL stat?

 

[Johntheo5]

To test which ever one trips the boiler, you think you would hear the boiler bubbling at that temp, my Firebird starts singing at around 90C, yours might be faulty and tripping too low.

 

[scottwhittaker]

It might be tripping at lower than 100C but it does trip the boiler and at a temperature higher than the desired temperature on the controls.
If I run the boiler for 10 minus and then turn the DHW dial down, the burner should shut off. The relay is clicking open but its not shutting the burner off. The stat seems to be the only thing stopping the burner which its supposed to do.

 

[Johntheo5]

Yes, the electrical schematic is pretty good, you would think poking around with your M.meter would show up something though.

 

[scottwhittaker]

Yes not something iv got much experience with sadly. I should learn! I think I'm looking for a live that will be live when I switch the boiler on at the spur (as it will want to heat it's water tank) but then shouldn't be live once the hot water is up to temp maybe