boiler behaviour,please let me know your thoughts.

[Post and beam]

1 hour ago, JohnMo said:

Nothing unsophisticated, just simple science,

I maintain that it is indeed unsophisicated. Becuase...

1 hour ago, JohnMo said:

if you throw lots of kW of heat at water it will overheat

The control algorithm cannot cope with this.

 

Remember, nothing i am doing is outside of the published operating parameters of the boiler. Forget whether or not my house is poorly insulated ( it is). or i have too many TRV's, or i dont want to run at a higher temperature in the house to mitigate the over production of hot water.

[JohnMo]

You are just operating the boiler and the heating system all wrong.

 

Running at the highest possible temp, then throttling everything via the trv's leads to the issue you have.  Any boiler would suffer just the same, even my very sophisticated Atag boiler, I was using last year.

[marshian]

1 minute ago, JohnMo said:

You are just operating the boiler and the heating system all wrong.

 

Running at the highest possible temp, then throttling everything via the trv's leads to the issue you have.  Any boiler would suffer just the same, even my very sophisticated Atag boiler, I was using last year.

 

Abso-f*cking-lutely this

 

It's like choosing an F1 car for a city commute or a Bicycle for an F1 race it's just nuts and because it's so nuts the boiler doesn't like it and says thank you - goodnight

[SteamyTea]

19 minutes ago, marshian said:

It's like choosing an F1 car for a city commute or a Bicycle for an F1 race

Tis easy.

 

 

[John Carroll]

Hi, Max Verstappen here, I do know quite a lot about radiators since they play a very important part in keeping my engines cool but also know how the rads work in my modest 4 bed house in Belgium.

All boiler manufacturers use a dT of 20C (and have a settable flow temperature of 80C/85C) to calculate the max flowrate through their HEX and still allow sufficient pump head to circulate through the system rads etc without having to install a LLH or the like. Bearing that in mind a T50 rad must have a flow temperature of 80C with this 20C dT to give its rated output, the rad full output may only be required at a OAT of say -7C, the rad output requirement then reduces with increasing OAT so the rad flow temperature can be reduced to give this output, this can also be done by installing TRVs but these need careful monitoring as they can quickly run out of control at high flow temperature and also require a boiler internal or external by pass or both, it can be easily seen below the effect of not reducing the flow temperature  and the very big effect on flowrates as was pointed out above.

 

 

 

Edited March 30 by John Carroll

[Nickfromwales]

9 minutes ago, John Carroll said:

Hi, Max Verstappen here, I do know quite a lot about radiators since they play a very important part in keeping my engines cool but also know how the rads work in my modest 4 bed house in Belgium.

Hi Max.
 

I doubt your integrity, I’m sorry to say, as I’ve seen your house and it is at least a 5 bed….something VERY fishy going on here.

[SteamyTea]

9 hours ago, John Carroll said:

Hi, Max Verstappen here

You were shit last weekend.

[joe90]

43 minutes ago, SteamyTea said:

You were shit last weekend.

No, your car was 🤷‍♂️

[SteamyTea]

9 minutes ago, joe90 said:

No, your car was 🤷‍♂️

One day I want to see the same car win every round.

Nearly got there with the one car I had a minor involvement with in 1988.

[John Carroll]

33 minutes ago, joe90 said:

No, your car was 🤷‍♂️

It was that darn 2965 that overheated the brakes on me but I had to blame the mechanic, Fangio had the same problem in 1956  but he still won.

[JohnMo]

44 minutes ago, John Carroll said:

It was that darn 2965 that overheated the brakes on me but I had to blame the mechanic, Fangio had the same problem in 1956  but he still won.

No it was the lack of airflow, to cool the brake enough that caused the 2965.

[John Carroll]

Back to reality, I would love to know what temperature triggers this 2965.

[JohnMo]

9 hours ago, John Carroll said:

Back to reality, I would love to know what temperature triggers this 2965.

I would have thought it combines a few things, temperature, rate of rise - because the fault code all relates to the system being dead headed, little or no flow.

[SimonD]

Hmmm, I'm still not sure why the discussion is still going down the route of dumping heat to the central heating system and boiler short cycling as a result of this. The intermittent behaviour being shown at the boiler is similar to the symptoms of a blocked dhw plate heat exchanger. The boiler shouldn't be programmed to use the CH to dump excess heat when calling for DHW heating as that's the best place to dump the excess heat.

 

Another similar process is when testing some makes and models of combis in service mode maximum output. Whilst the diverter valve switches to CH for this test, you also need to run the hot water taps to reduce instances of cycling during those tests as that provides additional cooling.

 

The fact that WB are trying to blame a CH system design error on a system that is working to within the operating parameter of the MIs is just total nonsense. If that were really the case then said knowledgeable heating engineer should be able to reproduce and demonstrate the issue to the customer. The WB engineer has kind of already admitted the problem. Now, redesigning, the heating system to be able to handle some excess heat on the occasion it's required may be a way to remedy the boiler design problem, but I would not be confident this would really be the solution simply because the error appears to happen on switching over to DHW, so any excess heat within the hex is an internal boiler issue and wouldn't have a pathway to CH under these circumstances anyway.

 

If the problem was indeed caused by the CH side, we wouldn't be seeing it occur on such an occassional basis given the system is running at max temps anyway. Remember the symptom is no hot water provision at all.

 

So the solution I think is for the OP to go back to WB to fix the problem properly, or sort a replacement because it's simply not fit for purpose. If the boiler has been supplied and fitted by the heating company, there is a fair claim to them to get the problem sorted out rather than the OP. They will probably be better placed to talk to their rep and technical support to resolve the problem. Personally I'd be asking for a different make of boiler built by a manufacturer that approaches boiler control and modulation more sensibly.

[dpmiller]

But can we be sure whether the error happens at other times or not?

[John Carroll]

If the boiler flow temperature can be noted at when in DHW mode then this will give a good clue to the performance of the primary & secondary HEXs even though the blocking is apparently occuring during CH operation, I know I've repeated this more than once but if 2965 is just triggered by a the flow sensor, or maybe a a separate primary HEX sensor, it would be nice to know its setting.

I posted these readings earlier from a 30kw WB CDI boiler which may give some clue, that boiler seemed to provide all sorts of info, don't know if this boiler has even got a return temperature probe.

 

Fouled PHEX, (DHW setpoint 55C). DHW flowrate: 9.2LPM. DHW Temperature: 44.5C. Boiler flowtemp: 71.5C. Boiler output 16.4kw Mains Temp:19.0C

NEW    PHEX, (DHW setpoint 55C). DHW flowrate: 10.0LPM. DHW Temperature: 54.5C. Boiler flowtemp: 64.5C. Boiler output 24.1kw. Mains Temp:19.6C.

Edited March 31 by John Carroll

[Post and beam]

On 31/03/2024 at 11:58, dpmiller said:

But can we be sure whether the error happens at other times or not?

The 'error'  is me having cold shower water.

Whether or not the central heating is being presented with no hot water supply on some occasions is, as previously stated, invisible to me and probably to anyone.

On 31/03/2024 at 08:27, JohnMo said:

I would have thought it combines a few things, temperature, rate of rise - because the fault code all relates to the system being dead headed, little or no flow.

This is true. Engineer demonstrated this when he was at our house. By opening the bathroom towel radiator TRV fully the issue did not occur during tests. 

 

 

[dpmiller]

18 minutes ago, Post and beam said:

The 'error'  is me having cold shower water.

Whether or not the central heating is being presented with no hot water supply on some occasions is, as previously stated, invisible to me and probably to anyone.

you're not helping us help you here...

[Post and beam]

3 hours ago, dpmiller said:

you're not helping us help you here...

I believe it is clear what the observed issue is.  I believe that to all practical standards it is not likely to be possible to detect if the CH water experiences the same pause to heating. And in any case the engineer has confirmed what he does observe and why. He said himself that opening TRV's ( at least one) does stop the issue at the hot water taps. He also agreed that changing our house heat behaviour, while effective, is not the answer to the problem and that the boiler should be able to cope with how we want/need to live.

But that Worcester Bosch would not be offering to replace the device for this scenario.

[JohnMo]

Well I suppose this thread has run it's course then. You know the issue, unwilling or unable to change your ways.

 

The other option is to throw the consumer protection option of "it's not fit for purpose" flag and demand its fixed by the installer, he would then get the manufacturer involved formally. Sitting on your hands, saying I know the issue and procrastination doesn't fix anything. Running high temperatures with lots of trv's doesn't help either.

 

I will now bow out of this thread.

[John Carroll]

 

I  popped a email to WB, they inform that.....

"The blocking code 2965 is generated when the heat exchanger temperature is greater than 88°C."

So irrespective of TRV settings or whatever, once the heat demand is less than the boiler's minimum output then if the target flow temperature is set to 82C then it is almost inevitable that the temperature will reach 88C since all gas boilers don't trip the burner until the flow temperature reaches target temp+ (at least) 5C. 

This setting is far too close to the WB approved max flow temperature setting of 82C.

 

I will now pose the question to them of whether there is a delay in clearing that alarm if still up on c/o to DHW.

[SimonD]

1 hour ago, John Carroll said:

 

I  popped a email to WB, they inform that.....

"The blocking code 2965 is generated when the heat exchanger temperature is greater than 88°C."

So irrespective of TRV settings or whatever, once the heat demand is less than the boiler's minimum output then if the target flow temperature is set to 82C then it is almost inevitable that the temperature will reach 88C since all gas boilers don't trip the burner until the flow temperature reaches target temp+ (at least) 5C. 

This setting is far too close to the WB approved max flow temperature setting of 82C.

 

I will now pose the question to them of whether there is a delay in clearing that alarm if still up on c/o to DHW.

 

Nice one! Good to get some clarity here. For reference I spent last week completely reconfiguring a system with a massively oversized boiler. This was a 30kW WB system boiler which I got modulating using opentherm controls with a converter and now working on PDHW with the opentherm controls rather that the WB diverter. On DWH set to max boiler temp of 82C it would sometimes get to over 90C as the cylinder reached target temp and the diverter valve closed and the system then relied on the bypass only for flow. But never did the boiler block as such, just tripped the burner as would be expected.

[John Carroll]

Interesting, looking at their reply again they said the heat exchanger temperature and not the flow temperature so there could be a significent difference in these depending on where the sensor is attached, could be something as simple as a faulty or badly attached blocking sensor?

Its a wonder the experienced WB engineer wasn't aware of this sensor's setting and location, i would chase them a bit further especially since this fault has been there since early on.

Edited April 2 by John Carroll

[MrPotts]

1 hour ago, SimonD said:

 

Nice one! Good to get some clarity here. For reference I spent last week completely reconfiguring a system with a massively oversized boiler. This was a 30kW WB system boiler which I got modulating using opentherm controls with a converter and now working on PDHW with the opentherm controls rather that the WB diverter. On DWH set to max boiler temp of 82C it would sometimes get to over 90C as the cylinder reached target temp and the diverter valve closed and the system then relied on the bypass only for flow. But never did the boiler block as such, just tripped the burner as would be expected.

This sounds interesting, I have been looking at ways to reconfigure my Greenstar 24i to do PDHW. I can reconfigure my existing s plan but I can't see a way to get the boiler to do two flow temperatures.

[SimonD]

33 minutes ago, MrPotts said:

This sounds interesting, I have been looking at ways to reconfigure my Greenstar 24i to do PDHW. I can reconfigure my existing s plan but I can't see a way to get the boiler to do two flow temperatures.

 

You've basically got 2 options here. Buy the optional WB diverter kit with a DHW cyllinder sensor and then get a friendly gas safe person to come and fit it. Then you need to add some controls so either weather comp sensor, and/or WB Easy Control. With this option you can only run a single heating zone because the weird way WB have decided to implement their technology means that if you have zones you forefeit modulation and then have to run relay on/off heating.

 

The second option is to get a Nefit opentherm/ems converter from the Netherlands and wire this into the boiler along with an openterm controller. This can then be configured using EPH CH4 combipack control with the CP4 DHW control to provide priority hot water, so 2 flow temps. With this you can have up to 6 heating zones. Now, this is not an official thing, but the Nefit is made by Bosch Thermotechnic, and although it has worked for me, I've found one of two mentions online where it hasn't worked on a specific WB boiler - but I don't know whether this is because it hasn't been wired up properly as these mentions were diy stuff.