Help with New Vaillant Boiler not staying on

[Irina Pri]

Dear All,
Please kindly advise, i don't know what else to do! Had new boiler Vaillant 424 heat only open vent boiler installed with new flue and filter, new pump, plus new Hive. Did full power flush of all 5 radiators before the installation. It has been 10days and boiler stil not working properly. I tried to sum up points below, could someone kindly give an advise as the gas engineer now says he doesn't know what to do and do not wan to refund so i can call someone else. I just bought this house as my first home and money very tight.
1. Boiler comes on if i set Hive to 26C and will work fine (max it reaches temperature of 24 so always stays on).
2. As soon as i lower temperature to 22 for example, the boiler will power down but will never come back up to maintain target room temperature, it will keep dropping down to 17C (I'm at work from 6am to 6pm so watching Hive on the phone).
3. Fault 23 comes back on every time i lower the temperature - the boiler will fire up but will stay on only for half hour or so.
4. Pump makes plenty of crackling noise on occasion, gas engineer was sure its air in the system so all radiators has been bled and system refilled a few times.
5. Vaillant advised Fault 23 related to flow and return temperature, gas engineer says he adjusts flow and return every time he comes in but boiler still will not come on to maintain set target temperature.
6. For me to turn it back on i need to first close all the radiators expect for one closest to the boiler and let it heat, then i start to open other radiators, if i restart boiler after the fault with all the radiators open the boiler will not stay on and fault message returns after a few min.
7. Hot Water works absolutely fine, it turns on from Hive and heats up no problem, i hardy have it on as I'm on my own so just an hour daily or 3 hours during weekend days.
Please could someone help me figure this out, i can't take any more days off at work to keep getting the gas engineer in and every time he leaves same issue comes back. Any other details you need please just ask i will do my best to answer.
Thank you very much!

 

[ShaunCorbs]

Sounds like it could be an air problem what’s the pump speed set to ?

 

[John.g]

F23 fault means the boiler flow/return temperature is >35C so probably air still in the system or pump speed too high drawing in air through the vent pipe possibly due to blockage where the cold feed joins the vent.
Can you post the boiler model, the exact pump model and mode/settings, (a photo of the pump LEDs etc while running will help) and a photo of where the cold feed and vent are tied in.

 

[Irina Pri]

Sounds like it could be an air problem what’s the pump speed set to ?

Thank you for your reply. The speed mostly was set to 3, however yesterday he lowered it to 2.

 

[Irina Pri]

F23 fault means the boiler flow/return temperature is >35C so probably air still in the system or pump speed too high drawing in air through the vent pipe possibly due to blockage where the cold feed joins the vent.
Can you post the boiler model, the exact pump model and mode/settings, (a photo of the pump LEDs etc while running will help) and a photo of where the cold feed and vent are tied in.

Thank you for your reply! I will get all the details you mentioned. Yesterday he checked flow and return temperature and it was 36C and 38C. He then called vailiant and they mentioned that boiler settings should not be on 24Kwh but should be on Auto, so he changed that and lowered pump speed to 2 (Grundfos UPS3). The pump still makes crackling noise but much less as i bled radiators again, but seems like air just getting in regardless how many times i bleed them. I set target temperature on Hive at 21 so will watch today if it maintains thought out the day, if not then what he changed yesterday did not helped and the boiler did not stayed on.

 

[Deleted member 120897]

Have you enquired with Vaillant if they could do a warranty call? It might be advisable to get the engineer or another to check the operation of the motorised valve.

 

[IrinaPri]

Sounds like it could be an air problem what’s the pump speed set to ?

Thank you for your reply! Speed on the pump mostly was set at 3, he lowered it yesterday to 2. Pump - Grundfos UPS3 15-50/65 230V

​

 

[IrinaPri]

F23 fault means the boiler flow/return temperature is >35C so probably air still in the system or pump speed too high drawing in air through the vent pipe possibly due to blockage where the cold feed joins the vent.
Can you post the boiler model, the exact pump model and mode/settings, (a photo of the pump LEDs etc while running will help) and a photo of where the cold feed and vent are tied in.

Thank you for your reply! i can check on details you mentioned. The flow/return yesterday showed 36C and 38C. He spoke to vailiant again and they mentioned that he should only set boiler to Auto rather then 24Kwh that he did, so that was changed, the pump itself Grundfos UPS3 15-50/65 230V stil makes noise but less loud as i bled radiators again yesterday, a little air did came out. He also lowered pump speed to 2. When i left today i set target temperature to 21 so will be able to see if boiler stayed on during the day, if tempreature will just keep droping then i know i will return to Fault 23 again.

 

[John.g]

Thank you for your reply! i can check on details you mentioned. The flow/return yesterday showed 36C and 38C. He spoke to vailiant again and they mentioned that he should only set boiler to Auto rather then 24Kwh that he did, so that was changed, the pump itself Grundfos UPS3 15-50/65 230V stil makes noise but less loud as i bled radiators again yesterday, a little air did came out. He also lowered pump speed to 2. When i left today i set target temperature to 21 so will be able to see if boiler stayed on during the day, if tempreature will just keep droping then i know i will return to Fault 23 again.

Are you saying that the return temperature is varying between 36C and 38C?, if so the flow temp must be 71C to 73C if its flagging F23 (dT 35C).
The UPS3 is a very powerful pump and IMO will create havoc on most vented systems as it will pump at a constant 6.4M head on speed3 and cause air ingress through the vent, even speed 2 at 5.2M can be excessive, I would suggest changing to (constant pressure) CP2 where the pump will run at a constant 3M head or/and try proportional pressure PP2 which starts at 3.75M head but modulates the speed to run at a even lower head of probably ~ 2.5M with 5 rads, you can try both modes yourself, its only a few button presses, continue to vent air, you could also hold a "glass" of water with the vent end immersed in it and see what happens to the level.

 

[IrinaPri]

Are you saying that the return temperature is varying between 36C and 38C?, if so the flow temp must be 71C to 73C if its flagging F23 (dT 35C).
The UPS3 is a very powerful pump and IMO will create havoc on most vented systems as it will pump at a constant 6.4M head on speed3 and cause air ingress through the vent, even speed 2 at 5.2M can be excessive, I would suggest changing to (constant pressure) CP2 where the pump will run at a constant 3M head or/and try proportional pressure PP2 which starts at 3.75M head but modulates the speed to run at a even lower head of probably ~ 2.5M with 5 rads, you can try both modes yourself, its only a few button presses, continue to vent air, you could also hold a "glass" of water with the vent end immersed in it and see what happens to the level.

View attachment 82520

the exact numbers they mentioned were D40 at 38C and D41 at 36C, sorry i should have wrote that, im strangling with understanding to be honest. These temperatures were after about an hour he worked on the boiler so vailliant said he needs to start again from cold system. I will do pictures today so you able to see/understand better the pipe work and will include whats on boiler display. Thank you very much for looking into this in detail.

 

[Deleted member 120897]

I think auto and 24kw settings are far too high for a 5 rad system, probably better with 10 - 12kw.

 

[IrinaPri]

I think auto and 24kw settings are far too high for a 5 rad system, probably better with 10 - 12kw.

Thank you for your reply! Could i please ask is this possible to do on this new boiler? The boiler i had previously was 16 years old but also 24Kw so i did like for like change. Is it possible for me to change the setting from Auto to 10/12kw or do you mean i need to get a different boiler with lower Kw?

 

[John.g]

Change d.00 max setting to 10 (kw) or so.

Also see if d.05 (boiler flow temperature) is settable, it states below that it isnt which seems strange, also note the anti cycling time, d.02.

Amazing that the flow/return temps are 38/36C, boiler firing??.
There is a d setting in some of these boilers where you can control the return temperature, it might be in one of the d codes if selected.

When f23 was flagged what did d.40 & d.41 read?.

 

[Deleted member 120897]

Thank you for your reply! Could i please ask is this possible to do on this new boiler? The boiler i had previously was 16 years old but also 24Kw so i did like for like change. Is it possible for me to change the setting from Auto to 10/12kw or do you mean i need to get a different boiler with lower Kw?

You’re welcome. No, i don’t mean swap the boiler. As above, it’s possible to range the heating side down, and shouldn’t affect the hot water delivery - let’s face it, there’s nothing to lose by trying it. I take it you missed my earlier post regarding the motorised valve?

 

[IrinaPri]

No, i don’t mean swap the boiler. As above, it’s possible to range the heating side down, and shouldn’t affect the hot water delivery - let’s face it, there’s nothing to lose by trying it. I take it you missed my earlier post regarding the motorised valve?

Will defiantly try it! Sorry, regarding motorised valves - both were checked and seem to work ok. Always responded even with previouse old boiler so i asked the gas engeener if i should order new ones as we upgrading the system but he was sure they work well still.

 

[king of pipes]

Post a few pictures of the boiler and cylinder could be he has the flow and return pipework be crossed ? worth checking , agree with the others drop the boiler to 12 kw and see if it makes a difference pump on a constant speed setting 2. Kop

 

[IrinaPri]

Post a few pictures of the boiler and cylinder could be he has the flow and return pipework crossed ? worth checking , agree with the others drop the boiler to 12 kw and see if it makes a difference pump.on constant speed 2. Kop

Thank you for your response! Understood - will take pictures tonight.

 

[IrinaPri]

Update- Same Fault 23 was on the boiler when I got in, I have closed 4 radiators and restarted the boiler, it only keep working if I open the rest of the radiators one by one after they got hot. Temperature on display keeps going up and down and radiator sign keeps flashing. Gas engineer coming back tomorrow to start again, is there anything else I need to tell him? ( I printed all your previous replies for him).
Thank you!
Irina

 

[Deleted member 120897]

I would get him every to check the flow and return temps under the boiler too using temp clamps.

 

[John.g]

Check the (downward) vertical pipe from the ABV (automatic balancing valve) is cold/cool with boiler running, it looks as if its set to max (ie closed) index of 0.5, 5M. It looks suspiciously as if its teed in to where the cold feed traditionally is/should be, alongside the Vent, if not a combined vent and cold feed, like mine. Try and see where the cold feed pipe is teed into the system it will be a 15mm pipe coming from the side (bottom) of the F&E tank, also check the obvious, that this tank contains water.

 

[king of pipes]

Where is the vent and cold feed connections ?

 

[John.g]

Can you post a photo of the very top of the boiler where the flow & return pipes are or/and ask you plumber to ensure that the flow pipe is connected to the pump inlet.


Edit: As per post#14.

 

[king of pipes]

This is how it should be piped it's obvious that the existing pipe has been adapted and only minor alterations made it not the best job in all honesty , we need to know where the vent and cold feed are connected ? If it's on the live side of the pump ? It could cause issues ? Kop

 

[John.g]

Is that a Spirovent in the photos?.

Its a Spirotec Filter.

 

[king of pipes]

Is that a Spirovent in the photos?.

No not a spirovent it's mag filter John. Kop

 

[IrinaPri]

Where is the vent and cold feed connections ?

My water tank is in the loft - is that what you mean by cold feed connections? (apologies im not very knowledgeable in this)
Vent is on the side of the house, sticking out from the wall.

 

[IrinaPri]

No not a spirovent it's mag filter John. Kop

That was installed together with a new boiler.

 

[king of pipes]

My water tank is in the loft - is that what you mean by cold feed connections? (apologies im not very knowledgeable in this)
Vent is on the side of the house, sticking out from the wall.

No the heating system cold feed and vent connected into the system pipework?? As the picture below

 

[IrinaPri]

Can you post a photo of the very top of the boiler where the flow & return pipes are or/and ask you plumber to ensure that the flow pipe is connected to the pump inlet.


Edit: As per post#14.

Can you post a photo of the very top of the boiler where the flow & return pipes are or/and ask you plumber to ensure that the flow pipe is connected to the pump inlet.


Edit: As per post#14.

Will do, sorry I didn’t thought of it. He is coming today at 4 to start, I got all the previous messages ready. He installed it on 10th March so it’s been a while and I really hope with all this help here he will be able to fix it.

 

[John.g]

My water tank is in the loft - is that what you mean by cold feed connections? (apologies im not very knowledgeable in this)
Vent is on the side of the house, sticking out from the wall.

Is there only one tank in the loft?? or are there two, one much larger than the other??.

 

[IrinaPri]

Is there only one tank in the loft?? or are there two, one much larger than the other??.

One big black tank at the loft. A water cylinder is directly under the boiler.

 

[John.g]

It looks like you may have a sealed system and a system boiler, not a heat only boiler, which I think refers to a vented system, you should see a red tank somewhere, probably near the boiler that may have a pressure gauge on it or the boiler may show a indication of pressure like 1bar to 1.5bar or similar?.

 

[IrinaPri]

It looks like you may have a sealed system and a system boiler, not a heat only boiler, which I think refers to a vented system, you should see a red tank somewhere, probably near the boiler that may have a pressure gauge on it or the boiler may show a indication of pressure like 1bar to 1.5bar or similar?.

Should definitely be Heat only as I specifically wanted like for like change, please see a few pics with boiler details. Plumber would have noticed that’s it was s y stem one I hope, I’m doubting everything now 🙁

 

[John.g]

The attic Tank may be your F&E tank for the boiler/system and you may have a unvented HW cylinder fed with mains cold water, if the hot water pressure/flow is the same as the cold water kitchen tap then probablay a unvented or look at the label on it, it should show the pressure.

 

[Deleted member 120897]

The numbers on Vaillants usually denote the boiler eg 424 heat only, 624 system and 824 Combi.

 

[IrinaPri]

The attic Tank may be your F&E tank for the boiler/system and you may have a unvented HW cylinder fed with mains cold water, if the hot water pressure/flow is the same as the cold water kitchen tap then probablay a unvented or look at the label on it, it should show the pressure.

Plumber did mentioned that he can install something for pressure but it can only be in the loft where water tank is so he said its not a good idea as i will have to go up there to change pressure. I'm sorry im so confused now with what i have and what it should be. All of you guys are amazing in writing all this details without even being there, it makes more worried that my guy been coming for 20 days now. He said today that he will maybe change the pump to UPS2 instead as its much more forgiving with old pipe system.

 

[John.g]

Plumber did mentioned that he can install something for pressure but it can only be in the loft where water tank is so he said its not a good idea as i will have to go up there to change pressure. I'm sorry im so confused now with what i have and what it should be. All of you guys are amazing in writing all this details without even being there, it makes more worried that my guy been coming for 20 days now. He said today that he will maybe change the pump to UPS2 instead as its much more forgiving with old pipe system.

He most certainly does not have to change the UPS3 because its too powerful, one can get any head required as shown above by changing its mode and setting. Its presently on speed 2 which is equivalent to a 5M pump, the head can be still further reduced in this mode to setting 1 which makes it a 4.2M pump, you can further reduce it to a 3M pump, CP1, or still further to PP1 which is only a 2M pump that isnt even powerful enough to circulate the water through your system. The UPS3 is only too powerful if the wrong modes and settings are selected.

 

[IrinaPri]

Attaching pictures for under the boiler, water cylinder connection and top of the boiler.

 

[Deleted member 120897]

Has he not fixed it today then? There should be an arrow on the circulating pump, can you see it? There’s a 22mm pipe that comes across your boiler and runs on the left hand side, is that connected to the hot water?

 

[IrinaPri]

Has he not fixed it today then? There should be an arrow on the circulating pump, can you see it? There’s a 22mm pipe that comes across your boiler and runs on the left hand side, is that connected to the hot water?

He canceled today, coming tomorrow at 9.
I found an arrow, it’s pointing downwards. The pipe, sorry, is it the one on the picture? It’s going down parallel water cylinder, but I can’t see where it’s connected.

 

[Deleted member 120897]

He canceled today, coming tomorrow at 9.
I found an arrow, it’s pointing downwards. The pipe, sorry, is it the one on the picture? It’s going down parallel water cylinder, but I can’t see where it’s connected.

Actually it’s the newer one to the left of where you’re pointing, but does look like it’s connected to the cylinder. Have you tried to range rate the heating or are you waiting for your plumber to do it?

 

[IrinaPri]

Actually it’s the newer one to the left of where you’re pointing, but does look like it’s connected to the cylinder. Have you tried to range rate the heating or are you waiting for your plumber to do it?

Oh sorry, white one is a condensation pipe, he installed it going into the bathroom wall and under the bath, there’s a water connection there, he added this tube to that connection.

 

[Deleted member 120897]

Oh sorry, white one is a condensation pipe, he installed it going into the bathroom wall and under the bath, there’s a water connection there, he added this tube to that connection.

Sorry,I didn’t mean the plastic one, I meant the copper one (as now shown in edited photo). As I said, I think it’s connected to the cylinder

 

[Deleted member 120897]

Did you try adjusting the heat output?

 

[IrinaPri]

Did you try adjusting the heat output?

No, Im honestly straggling to understand any of this, I don’t want to press something and make it worse. If he can’t fix it tomorrow, I will look for someone else as I find it very strange now that he hasn’t checked on any of the issues you all mentioned and it’s been over 20days since installation.

 

[Deleted member 120897]

No, Im honestly straggling to understand any of this, I don’t want to press something and make it worse. If he can’t fix it tomorrow, I will look for someone else as I find it very strange now that he hasn’t checked on any of the issues you all mentioned and it’s been over 20days since installation.

It wouldn’t make it worse, it would either fault again or help with the issue, but might as well leave it to him tomorrow though if you’re not comfortable.

I’m not sure if I can help explain it any better, but the boiler flow and return temperature are too far apart, which suggests several issues which have been mentioned.

 

[Deleted member 120897]

Any joy @IrinaPri or was it another no-show?

 

[IrinaPri]

Any joy @IrinaPri or was it another no-show?

Thankfully he came, he started with cold system, changed boiler to 12kw, amended pump setting as per above, set over run on a pump to 5min. All radiators were open, the boiler did not go to high flame straight away and no fault 23 came on after turning on the boiler, after 45min all radiators were hot and only then boiler went to high flame and then stayed at around 71C. I’m keeping heating on for the weekend, but on Monday will see if everything works - I will set Hive to 20 (it’s 23 now) and hopefully boiler will fire up and stay on to circulate and maintain the target temperature. Thank you again for your advice, I will update on monday hopefully with good news! Have a good weekend l!

 

[IrinaPri]

Update - You guys are most amazing professionals- the boiler stayed ON 🥹 Thank you all so very much, I’m so glad I decided to seek help here and it’s obvious now that my guy unfortunately does not have enough experience otherwise he would have try all this weeks ago.
At the moment temp on boiler 75C and holding, I set hive to 23C an hour before coming home and radiators all hot now and Hive temperature rising. The pump however still makes noise (video hopefully will upload below) not constant but often. I will keep an eye on it.
Again Thank you All for being so kind!!

 

[Deleted member 120897]

Maybe try the pump on a lower speed setting?

 

[IrinaPri]

Maybe try the pump on a lower speed setting?

Morning, ok, it’s still on 3. Will change it to 2 and hopefully noise will disappear, I thought it’s last remaining air and will make its way up at some point.

 

[king of pipes]

Speed 3 is to high 2 is more than enough speed 2 should do it really ? Kop

 

[IrinaPri]

Speed 3 is to high 2 is more than enough speed 2 should do it really ? Kop

Can I please check- I need to press white Arrow once til it has 2 orange lights and says II ? Do I need to turn anything off or just press it while pump and boiler on?
Thank you,
Irina

 

[Deleted member 120897]

Can I please check- I need to press white Arrow once til it has 2 orange lights and says II ? Do I need to turn anything off or just press it while pump and boiler on?
Thank you,
Irina

Yes press the button until there are 2 lights on, don’t think you can do it without the pump running, so yes leave everything on with a demand.