Need help with a faulty Glow-worm boiler?
We depend so much on our boilers day in and day out, so it’s easy to forget that they’re even there, just doing their jobs – that is, until they break down and you’re left in the cold with no hot water or heating!
I know how stressful it is – I’ve been helping people in the Edinburgh area deal with faulty boilers for over 20 years, and I’ve had many a run-in with Glow-worm boilers in that time.
That’s why I thought I’d put together this handy blog post, to help you diagnose the problem and determine whether or not you need to call in an expert – as well as to give you an idea of how involved the fix will be!
NOTE: It’s important you DO NOT try to fix the problem yourself, unless it’s a very simple fix such as topping up water pressure or defrosting a frozen condensate pipe – for everything else, always call a Gas Safe registered engineer.
About Glow-worm boilers
Glow-worm is part of the Vaillant Group, and the company has its own dedicated service engineers to cover both Glow-worm and Vaillant boilers. Parts are easily available and reasonably priced, and they are a popular option for many of my clients.
The good news is that although Glow-worm is a budget boiler, it’s NOT a boiler brand with numerous faults and a bad reputation. The parts are usually easy enough to source, and from my experience you can usually replace just one part and the boiler will fire back up – unlike some other budget brands with simultaneous faults.
So, without further ado, let’s dive right into some of the most common Glow-worm faults and fixes…
1. Fault code F16 (Ci models)
If the code F16 flashes up on your Glow-worm Ci model, this indicates a flame detection fault with your boiler. It could very well be that the boiler itself requires a service, and the probe needs cleaned or replaced. Please note though, I’ve also seen this code when the boiler is not igniting due to no gas coming through the pilot assembly,
The Fix: Check the pilot assembly is clean and free flowing from the gas valve. If so, replace the flame detection probe and lead.
2. Fault code F9
Next is the dreaded F9 code. The main problem here is that it’s a very generic code which can point to a few different faults relating to pressure, circulation and diverter valve issues. First, check your pump is running, then check all electrics from the circuit board. Is the boiler going through the correct sequence?
In my own personal experience, and usually also with communication from Glow-worm, this fault code has actually been caused by a sludged up plate heat exchanger – this can happen when the system has not been cleansed or adequately flushed.
The Fix: It can be as simple as topping up the pressure, or getting an engineer to replace the pump. However, as I mentioned above, I’ve found Glow-worm boilers are very sensitive to sludge build-up, so flushing the system may be advised.
TIP: Whenever I do this for my clients, I usually fit a magnetic filter and on one occasion, I’ve also replaced the thermistors (in the case of black iron oxide coating the sensors) – all good, and no second call-backs.
3. Fault codes F1, F3 & F4 (Flexicom CX range)
Codes F1 and F4 indicate an ignition fault, however F3 is a fan speed fault. However, if the fan does not come up to speed, you have an ignition fault, anyway. I’d recommend getting a multimeter out and checking your readings from the PCB to the fan. Also, check ignition leads and power from the PCB.
The Fix: An engineer will either replace the fan or the PCB. You may also need to replace the ignition leads, depending on the results you find from the multimeter readings.
4. Fault code F14 (Flexicom CX range)
If you were to look at the service manual, you’d find this fault states there’s a defective gas valve. However, check there is power from the PCB to the gas valve. If not, it’s not the gas valve at all, but either the PCB or the wiring harness.
The Fix: An engineer will likely either replace the gas valve or the PCB/wiring harness.
5. Fault codes F61, 62, 63, 64, 65, 67 (Betacom)
This is quite a range of faults with the Betacom models, however, all of these faults indicate there’s a problem with the main circuit board, or PCB. Before replacing the board, I would test the whole sequence with a multimeter. It could be a faulty connection from one of the components to the board, or the wiring harness.
When servicing a boiler, it’s not uncommon for a cable to get caught in the casing when putting back together, and this can cause a short circuit indicating a fault at the PCB.
The Fix: If there’s no joy after checking the sequence and connections, an engineer can replace your PCB to get things working again.
Conclusion
There we have it! Five common faults with a Glow-worm boiler. Luckily, Glow-worm is quite a reliable brand, and with parts easily available, it’s usually worth it to pay for repairs – unless you have a particularly old model.
I hope this blog post has given you a better idea of what might be causing the problem with your faulty Glow-worm boiler, but if not, please feel free to either leave a comment below or get in touch directly. I’ll be happy to help!
Light on ignition wirking still no warm water boiller gone quet
I’ve just purchased a new property where a Glow-Worm Ultra Com2 24cxi has been installed. It’s fairly new and the handheld programming device seemed simple enough – however despite following the manual/instructions, I am unable to program the water to come on/off at specific times. This is despite the manual making clear this should be an option.
The previous owner has suggested that you can simply leave the water constantly without any issues but given I will be out during the day 5 out of 7, this seems perverse and a waste of money/energy.
Any help or advice would be greatly received!
Thanks
It’s a combi boiler so it heats the water as you use it. The instruction booklet appears to be wrong as there is no function on the handset to programme times for heating water only the temperature and if it’s on or off. You are not heating water unless you run your taps.
Heating but no hot water.
Did you sort this? Got same problem
Hello I have a glow worm hideaway ff when it gets to temperature and cuts off it won’t start again by itself I’ve tried another pcb board new danfoss 102 new thermistor new Honeywell t40 still won’t start even when cooled down in have to reset boiler itself any information would be grateful thanks
Did you solve this? I have the same problem
We have a Glow Worm back boiler. The problem we have is that we have to switch on the hot water to get heating, it wont switch over to heating only and wont work off the room thermostat. Any thoughts?
My glowworm boiler ultacom 24cxi has got 1.9 pressure but when I run my hot tap I get no hot water the flame cums on then goes straight off can’t get no hot water what u think it cud be ?
hefle
Get an intermittent buzzing noise from 2 yr old Glow worm combi which stops when hot water is run.
my boiler wont work via the thermostat – what can i do
I had an F1 fault on glow worm boiler which resolved after I raised pressure and reset boiler. Boiler failed again the next day this time with F4 fault. Resetting didn’t work this time but pouring warm water from kettle on the outside pipe that leads from boiler to rhone pipe cracked the ice that had built up inside it . Boiler restarted after that! Will be insulating the pipe to prevent boiler failing when I need it most ie when it’s bloomin freezing outside!!
My heating is working fine but my hot water runs hot, then cold when I run the shower or bath. Any ideas to help please?
Ray – same problem .
I get this every few years. In my case the heat exchanger is getting blocked by corrosion in the central heating system. I have to remove the heat exchanger and clean it out. Its a very fiddly job to get the heat exchanger out and you end up with water everywhere, but it is do-able. Be careful not to loose the sealing washers.
Boiler ran out of gas on meter pilot light us out the pump works when switched on but there is no nothing on the display to say what it could be any ideas..thanks
Hi. I have a glowworm cx30i around 10years now.
I don’t use it on a timer only controlling the heating by thermostat.
When the thermostat is reduced to off the boiler keeps coming on intermittently and runs for 5_7 minutes then it will go off for a while and do this continuously.
Hotwater works fine and heating aswell when thermostat demands.
System as been cleaned and inhibitor added.
Do you have any thoughts or pointers please
Check your hot water dial is not set to eco as this will enable the preheat
Gloworm Gas boiler 330 cuts in every few minutes the CH water then ranges from 64 to 74 degrees. This takes place during the off period from the UP2 timer. How can I correct.
Hi, I have a Glow Worm Ultra Power 100 SXi which is 4 years old. It has started to fire up in the middle of the night (the timer is set to be off between midnight and 6am) and the water tank overheats, causing the safety discharge valve to open and the hot water then goes down the tundish to outside. No fault codes appear, on the display. The only way to “fix” this, when it happens (generally between 2 – 3 am), is to turn the boiler off at the mains and turn it back on when I get up. This is an intermittent fault and happens maybe once a week. Any help would be appreciated, before calling a plumber in.
Hi I have the glow worm 30ci it keeps losing pressure even when it is turned off from the main switch on the boiler any ideas what’s going wrong
Hi. My glowworm 24xi has a flashing red light and pressure of 0.4. I have tried repressuring it and it’s not working. Please help
Thanks for creating your blog – it’s been very helpful only I sa it too late – my Flexicon had F1 & F4 showing and I called a plumber who sent round one if there guys who quickly diagnosed the fault as a failed heat exchanger – I said it’s ignition and he disagreed telling me he could fix it by replacing the heat exchanger for £1500 but it would take a week to 10 days for the German made parts to arrive but J would be better off getting a valiant at £2400 fully installed and would be on the same day – I was ill and didn’t know what to do so went for the expensive option – now I feelI have been robbed. Any comments ?
My mum has a Glow worm Hideaway FF boiler, and recently it’s had some problems lighting. A replacement circuit board was fitted to see if that would fix the issue. The boiler will now light but rather than start with the timer it will pick and choose when it wants to come on and she finds she has to over-ride the timer to try and start it. She get’s a flashing light on the ignitor saying the burner won’t come on. Is this a known problem? How can she get confidence that when the timer comes on that the boiler will ignite? Was the circuit board a red-herring and could something else have created the initial problem?
Hi I have a betacom 30 ( 2007 ) which appears to be asking for hot water all the time. I have fitted a reconditioned pcb but no change, can any one help with a diagnosis.?
My glowworm boiler isn’t showing any fault codes but we don’t have any hot water or heating, we have had fault codes previous to this, mainly f1, any ideas what this could be please
I have a glow worm 80pp, I had to recently change my pcb board, however since then the the boiler works, but now have a new fault. Pilot light on but heating & water go off whilst on timer or when on demand I have to manually fire up the boiler, that worked for few days now it boiler won’t come on although boilers on and so is the pilot, any help will be appreciated please.
boiler recycling in my experience is due to a sticky diverter valve. turn system off and move valve back and forth manually. That should fix it.
The pressure goes up and the boiler cuts out and a red fashing light what wrong with it
My daughter has moved in to a property and can only have the heating on 30 or off. No in between. She’s 3 months pregnant & has an 18month old. Also suffers with asthma. On prepayment meter & cannot afford to heat the house.
Water tap too tight on glowworm boiler needs refilling any suggestions please
we have a G/L Flexi 18. the boiler will not come on when required, however I have turned off the mains and one the mains are turned back on the boiler will ignite and no further problems, that is until the next time. Done the same three times now, never had the problem before.
Hppe you can help.
I have a glowworm 30hxi and have just had a new grundfos alpha 2 pump fitted to replace the old alpha.
The pump works however although it is turned off as normal by the boiler there still seems to be a small current leak to the pump resulting in a flickering display. Has anyone experienced this. The pump is not faulty as this has happened with 2. There is no fault code on the boiler.
John
My Glow worm 330 boiler ( condensate) is 13 years old, and my visiting service engineer is trying to suggest that it’s time to replace the boiler. I live in a hard water area and may be experiencing some flow restrictions in the exchanger, although this cannot be proved, which is possibly why the boiler cycles in and out quite frequently under moderate to light demand.
Is 13 years old considered too old in your opinion, and would I save money by fitting a modern boiler ?
I have a Glow worm Flexicom cx previously had its annual service, I was having to top pressure up as it was flashing F9 service engineer replaced a valve it now only runs for 2 hours then knocks of to flash 0-5 hence I have to switch everything off to top it up to get a couple of hours heating this is frustrating as it is freezing in the mornings as it doesn’t operate especially when It’s on timer for 5-30 am and obviously there’s no hot water when this occurs
I’ve got glow worm flexicom 30cx. The central heating is working but no hot water. Any ideas will be much appreciated. Thanks
My Glow worm Fuelsave F of some 20 years of age works O k but the temperature of both water and heating will not rise above base heat.
The fans tarts the system with a nice blue gas glow, It will run for a short time but then switches off for a time before starting again.
What is the likely cause of this problem and what will it cost to fix please.
Thank you Terry Lyden
Fog horn sound in the morning coming from boiler !!! Lasts up to half an hour,worse if cold outside!! Any ideas??
Its a brand new glo worm com I
I have a Glow-worm Flexicom 30SX that won’t start on very cold mornings. I’ve had this problem twice in the past. Both times it was the pressure sensor at fault. The solution being to clean it or replace it. However with this cold weather it’s now doing it again. Just had the boiler serviced and the sensor wasn’t that dirty, and it’s fairly new, although the engineer noted it was reading 0.3 bar high. A faulty sensor might seem the obvious culprit but it’s difficult to do a diagnosis when the system is warm as the fault only occurs when it’s very cold. Any ideas would be very welcome.
Hi, wonder if anyone can help? Have a Glowworm 24cxi (G.C. No. 47-047-23) Combi Boiler, an old model from 2004/5. It’s suddenly stopped working. Red light comes on with code F and the pressure is reporting 0.0. Is there anyway this unit can be saved and brought back to life? Appreciate advise from experts or users who experienced the same problem. Thanks.
Just had a tech come over for a f43 on a flexicom. He mentioned that its usually a water flow issue and to check the water pump. Alas, we checked the pump and found it was not working properly.
Hope this helps anyone with an f43 error.
Hi, my friend has got an Ultrcom 18hxi, currently it is tempermental to get going?
when they call for heating, the boiler doesn’t fir, but if they turn the gas hob on the boiler will work? Trouble is if they turn the hob off the boiler will go out???
Its a communal system of LPG Gas and the regulator at the meter has been changed 5 times????????
any one got any ideas???????????
My glow worm ultimate switches on but then goes off after 30 minutes the radiators have warned up & the water but the boiler then won’t go on again till about 10 hrs later the front of the boiler gets hot.it’s a wall mounted boiler
no light on the lcd at all, help.
I have a 10 year old Glow worm 12hxi boiler, last serviced 2 years ago. Although there isn’t any fault codes registering on the boiler display, the floor underneath the boiler is damp when the shower is used.
This is a recent small problem any thoughts on why or what parts are required?
I’ve got no power to my boiler ??
I’ve got cold water dripping from the bottom of my boiler when I turn the heating on and it reaches about 62 degrees but not when I turn the hot water on . My boiler is a flex icom 35cx , please say it’s a quick and easy fix
check out the condensate system. It’s a white box at the back with two corrugated plastic pipes feeding it. It often overflows causing the water to run off the bottom of the unit
Comment my Glowworm Ultracom boiler is leaking, it is about two and a half years old
Cannot get heating on and no fault listed
I have recently had a Glow Worm boiler fitting 6 months ago.
Once the thermostat is turned down the boiler will not fire up again unless I flick the switch on and off. It’s like it has default to a standby mode.
I have recently noticed if I turned it back up within the 30ish mins from turning it down it will then fire up.
The same is happening on the water side of it.
Please help!!
Boiler shut down an inline fuse is ok an main fuse is ok but no power to boiler
Boil has no power after a power cut
Hi guys I have a fault on my glow worm xtra fast 120 e it’s coming up as 14 ff I’ve looked this up and it’s saying central heating flow temperature >97c can anybody tell me what this means please
Hi, I have a little box (about 3″x3″)under my boiler with a small grey button and two led lights. The little green light at the top of the two keeps turning off and when it does I have no heating, it comes on when I press the little grey button but only for about 30 minutes. Hot water is working as normal when I turn on the tap. No fault codes on the actual boiler. It’s a flexicom 24cx. Any advice please?
Hi! I suspect I have sludge in my traditional system as draining attempt was v. Slow. Problem now is that the Glowworm Ultracom HXi (British Gas 330) only runs for 3 seconds, then flashes code F5, closing down. Please help! Dave.
I’ve just moved into a new house with a glow worm boiler it is not a combi boiler. The pilot light is on but it is not lighting up when the heating or hot water turns on. What can I do?
My flexicom CX30 failed and fault 9 was shown. A service engineer after fixing the fault, said to be a seized water pump, has suggested a new pump be fitted and has quoted £411.01 + VAT to supply and fit one.
I see from ebay that new pumps are available at prices ranging from £80 to £170, thus it would seem 4 to 5 hours at their hourly rate of £72 has been allowed for fixing, is this about right or am I being taken for a sucker?
Awesome site. Thank you
Boiler makes a clicking sound continually when on . Only a month old .
Hello. My boiler has been having fault F23 since being installed. There have been numerous engineers look at it and every part has been changed and its still happening. Next thing to try is flush out the entire system but I have a feeling this wont work. Ideas why this is happening and what should/could be done?
My Glow-worm 18r-A boiler is 18 months old and has come up with fault code F28. What does this mean?
Please please please someone help????????
I’ve had F12 show up and i got Engineer in who stayed maximum 10 mins (£60 later)…… to tell me it was my PCB that was gone.
Got a new PCB. Fitted it now shows fault code F10 flashing.
Is thus something that I could repair myself & if so….how???
Have a new Glow-worm combi fitted in Jan 2017. It shows water and heating off, but the heating stays on all the time. I have to switch the whole system off and just put it on when we need hot water. Guarantee for next 4yrs but can not get the heating eng to come and look at it