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.