Glow Worm 24CXI No Pre-Heat

[edlin]

Hi, wondered if anyone could shed some light on my issue. I've browsed google but unable to find the answer. My GlowWorm 24 CXI Domestic hot water temperature is significantly lower then it should be, I've had the boiler for five years and this is the first problem encountered. Everything was fine up until yesterday when I noticed the temp had dropped by at least 10 degrees but the output pressure was still the same (Fantastic Pressure). There are no fault codes reported, the central heating circuit is working without issue. The Domestic Hot Water dial is set to ECO, so within the Pre-Heat segment but the boiler is no longer firing at random times to charge the vessel. I've power cycled, rotated the DHW dial in and out of Pre-Heat and nothing. I initially suspected the thermistor before I realized there was no obvious pre-heat. The boiler now sits dormant unless the CH demand triggers or I use the hot tap. I've got a baby coming in 4 weeks, money is tightish, guidance from one of you pro's would be much appreciated. Thankyou.

 

[southcoastboile]

one thing you could check is put your hand on the flow pipe to the heating when system is cold, turn on a hot tap and see if it gets hot, if it does its the diverter valve. If not then i would suspect plate heat exchanger is sludged. Even if the preheat is not functioning it should still get hot when you put a demand on the hot tap. You can check the instructions as its normaly possible to turn the preheat on or off which you can do yourself but you will need a gsr engineer to find the fault, hope this helps

 

[diamondgas]

:welcome: to the forum edlin 🙂

With or without the pre-heat your boiler should perform according to certain parameters described in the manufactures instructions ... i.e. is should supply a certain temperature rise with a certain flow rate of water! This time of year most 24kW boilers will struggle to heat the cold water sufficiently unless the flow is reduced ... IMO

Try turning the hot tap back a bit and see if that makes any difference!

Regards the pre-heat, I'd have to do a bit more digging to see if your boiler has that function ... 🙂

 

[edlin]

Thanks for the reply, will give it a go. Pre-Heat is defined on the DHW knob on the front of the boiler. Its always been set to ECO which sits inside the pre-heat segment. I've pushed the knob fully to the highest setting and the boiler still doesn't fire when idle. It's just odd that it doesn't fire at random times like it used too. I'll definately check the CH output when the hot taps running, just got to let it cool down a bit.

 

[southcoastboile]

is it the one with the orange screen? if so i'm sure there is a sequence of buttons you can press to turn it on or off. Have you checked about the preheat in the book?

 

[southcoastboile]

just read diamond gas's post, he is correct although if its better with less flow it could also point to sludged plate heat exchanger, you may find burner cuts out at a lower flow rate, if so this is likely the fault although dont turn it to low as the flow switch won't activate

 

[edlin]

Nothing's changed with the boiler in the previous 5 years of ownership. The boiler has pre-heat, it would fire at random times of the day to produce instant hot water. The high temp has always been consistent irrespective of outside temp, particularly notable last year when the temp dropped to -16. The pressure from the Kitchen tap and shower is strong, I would always have to turn down the temperature to prevent scolding. The shower and kitchen tap in the last 24 hours never gets to that point, it's hot but not unbearable. The only obvious symptom to me is that the boiler no longer does that pre-heat charge at random times during the day even though the DHW dial on the front of the boiler is still inside the Pre-Heat section (I've adjusted it to make it even hotter, tested, moved it back tested etc). The boiler would click, I would assume trigger a relay when it pre-heats, that has now gone.

 

[southcoastboile]

there is a fault with it as the preheat function will not effect the temprature, all it will do is preheat the water so it comes through faster. It should still get hot regardless if the preheat is functioning or not as diamond gas has said

 

[edlin]

Yep, its got a growing orange ring around the dial, Clockwise rotation, from your 7 Oclock to 11 Oclock is a varied output temp with no pre-heat. 11 Oclock to 5 Oclock is the same temp range but with pre-heat. There is a section within pre-heat called ECO which is recommended by Glowworm. The dial up until today had never been moved from ECO. The boiler would always fire up for about a minute to provide that on-demand heat as descibed by Pre-heat. I don't know what the trigger for that is, temp perhaps, but it would always do it consistently. The system has been fine for 5 years but in the last 24 hours there has no evidence of the boiler firing unless I put demand on it from a tap or trigger the CH via my thermostat. Would sludge in the heat exchanger stop Pre-heat from firing though, just sounds odd to me.

 

[southcoastboile]

no it wont, you need it looked at by a gs engineer. Dont worry about the preheat, its not causing the fault. Waste of money if you ask me and i would leave it off anyway if it was my boiler.

 

[diamondgas]

edlin it's more likely a diverter or plate heatexchanger issue............... if its been "all of a sudden" then I'd be edging towards the diverter .... try the test suggested from cold 🙂

However the pumps on these are also dubvious depending on age so it may be worth gettin someone in ... However if you'd like to do a simple check so as not to waste your pennies you can check the boiler's parameters with a thermometer, stopwatch and measuring jug 🙂

 

[edlin]

Ok, so looks like the Exchanger is sludged, but do you think that would account for the demise of pre-heat?

 

[edlin]

Thanks DiamondGas, will do. We are talking about the CH output to test? I'll let the pipes cool down a bit. The pressure from the tap when running hot doesn't appear to of changed though. Its still banging it out nice and hard as it always was. i'm just really confused about the pre-heat though. Would you expect something like that to stop functioning if the exchanger and / or diverter was the cause.

 

[diamondgas]

Ok, so looks like the Exchanger is sludged, but do you think that would account for the demise of pre-heat?

to check if pre-heat is working or not turn the boiler off, run the hot tap till it's cold then turn the boiler on without a call for heating. If the boiler fires up then the pre-heat is working fine 🙂

 

[diamondgas]

Thanks DiamondGas, will do. We are talking about the CH output to test?
.

Nope 🙂 You can check whether the hot water is working as per the manufacturer quite easily ... Your boiler will raise the temperature of the cold supply by 35 degC when the water flow rate is around 10 ltr/min.

 

[edlin]

You know up until today when I checked the installation guide, I didn't realize the consequences on cost with pre-heat. If I read things like most men don't do I would of turned it off 5 years ago. Thanks southcoastboile for the time, I will check the diverter when the CH has cooled a bit. Before I looked into it further, I had hoped it was the thermistor but then realized about the loss of pre-heat. I can't help but feel the PCB is questionable too but you're absolutely right, the Hot water temp shouldn't be different to what it was 24 hours ago irrespective of pre-heat. What ever happens I'll make sure the outcome is recorded on this site for others. If the diverter isn't the issue and I need to get a GS in, can anyone recommend someone in the Towcester, Northants area. I've never been lucky.

 

[diamondgas]

edlin you can post a request here [DLMURL="http://www.ukplumbersforums.co.uk/im-looking-plumber-gas-engineer/"]I'm looking for a Plumber or Gas engineer.[/DLMURL] and 'vet' B4 hand :l0l: good luck 🙂

 

[edlin]

You're a diamond. Just to let you know, the power off, run of the hot tap until cold and then power on fired up the boiler. It fired up again five minutes later on its own accord but has stopped again. I've now got an issue with the pressure sensor, or at least assume it is as I've lost .2 bar in 2 hours. The rads are perfectly fine, no cold spots, no air trapped following a bleed. I've had to fill the system in the past after loosing .2 bar due to a weeping TRV but there is no obvious movement of water when I turn the filling loop now. This would suggest I'm already pressurized?, the system is also cool. I disconnected the control wire to the pressure sensor and received an error code, reconnected and got .4 bar and then .5 with a flashing warning light. It wouldn't go back to .6 bar as displayed prior to reseating the sensor wire. I power cycled and got .6 again. It has to be pressurized as the filling tap doesn't move water (It's so obvious normally with the sound of running water). Could it be that all this is due to a defective pressure sensor or am I looking at multiple failures.

 

[diamondgas]

edlin .... krikey 🙂

you're probably messing too much mate! Why take the lead off?

 

[edlin]

🙂 I just wanted to see if the reading changed. Anyway its back now, the boiler reading at cold is .6 bar. Can't be right, I've opened the filling tap and the boiler won't accept anymore water. I've made another discovery, something I noticed the day of the issue and overlooked. Mains pressure has increased, the toilet is significantly more noisy when it's flushed and you could strip paint with the cold tap when its fully opened. You can tell the difference with the noise from the boiler when the hot tap is fully open, that wasn't evident before all this happened yesterday. Anglian Water must of upped there pressure, could this be my issue?

 

[southcoastboile]

no problem mate, one thing ive learned is don't touch anything on boilers that you dont need to, you will cause more dammage i.e the pressure sensor you have been playing with. pressure will fluctuate up and down depending on the temprature of the system, should be 1-1.5 bar cold and just over 2 when hot. If this is the one with the blue knob you turn to top up the pressure then it can sometimes get stuck internaly so won't top up. If not it will be the two white lever types under the boiler that you need to turn. Sounds to me you may have a few faults. Check diverter valve as discussed. If its not that then my money is on the hw heat exchanger. Get a gas safe engineer in, try check a trade and look at the feedback, this may help you to decide on a good one.Hope you get on ok, update us to the outcome when its fixed :smiley2:

 

[southcoastboile]

to respond to your previous question the boiler is designed to work at a certian flow rate, this can be tested by refering to mi and using a flow cup. easy way to tell if this is why is to turn the tap down slightly and see if you get hot water, if all ok then you could turn the iscolation valve on the hw outlet slightly to decrease the hw pressure.

 

[edlin]

Cheers to you both for your time spent on this. one of my neighbours who I've just spoken has exactly the same issue with DHW temp. Her husband like me has been scratching his head all day trying to figure out why there boiler DHW had dropped in temp. looks like Anglian have got an issue in the Northamptonshire area, pressure is so so high, you could strip paint off a car with it. The panels are back on, I'll monitor the situation and if unchanged contact Anglian tomorrow. Too much of a coincidence I think.

Its the Blue type filling loop, perhaps the excessive pressure is preventing the valve from opening? The book states to fill to 1 bar.

I will get back to you all tomorrow with the outcome from Anglian.

 

[diamondgas]

Increase in your mains pressure does sound like the cause for your concern edlin .... It'll increase the flow rate through the boiler decreasing the heat pickup as it passes through your boiler.... The fill loop on these are notorious for seizing alas! Usual suspect is a thing called the reduced pressure zone valve! 🙂