boiler behaviour,please let me know your thoughts.

[John Carroll]

Exactly, the boiler flowtemp can be set to 82C and if/when it does exceed this or any target temperature then the burner will cut out once/if the temp goes 5C higher, pump continues running to reduce the temperature to enable the boiler to refire again after a suitable (anticycle) period, all standard practice.

When you c/o to DHW then cold DHW has to flow through the plate heat exchanger before the boiler refires and as long as the DHW flowrate is greater than 3.3LPM then the DHW will not reach the overtemp setting of I think ~ 85C/90C on say 65% fire up ignition conditions.

 

If, as I asked previously, there are no problems with repeated DHW operations? then looks very much like a poor design feature if it prevents the boiler from firing until the (CH) recycle time or whatever has elapsed.

Also fault code 2965 should not be flagged under the above conditions

Edited March 26 by John Carroll

[dpmiller]

1 hour ago, Post and beam said:

No its 15mm.

all of it?

[ProDave]

1 hour ago, JohnMo said:

Agreed, but trying to shove 20kW of heat via a couple of radiators and does not/isn't working, your boiler overshoots and locks you out. Once you are locked out, the boiler does not fire for heating or DHW

The point everyone is missing is this is DHW demand.

 

Yes I can understand the modulation and PID limitations when heating, but the point I would be banging on abut is you have turned on a tap, it should be heating DHW with a completely different set of parameters and control algorithm.  The fact it refuses to do that because it previously locked out doing something different thing is a FAULT with the programming.

 

When it switches to DHW it should completely ignore what it may or may not have been doing previously and get on with the job of heating the hot water. Anything else is a design fault.

[JohnMo]

2 hours ago, Post and beam said:

code is very specific '2965' to be precise

A quick read of the manual

 

The B is 

 

Fault category B (blocking faults)

Blocking faults result in the heating system being shut down temporarily.

The heating system restarts automatically as soon as the blocking fault is removed.

 

15 minutes ago, ProDave said:

The point everyone is missing is this is DHW demand.

 

Not missing point at all.  It's a single boiler, that has a blocking code, this will prevent it firing up for any reason. The CH flow fault needs to be resolved with the flow through the boiler, otherwise it will only continue as it is.

 

Would suspect the following occurs

 

Trv's are open, boiler flows no issue, does heating and DHW as normal, trv's close in or fully closed, there is not enough flow through the system left open (2 rads and 15mm pipes), boiler gets blocking code. Boiler does fire for any reason while blocked.  Rooms cool, trv's open, heating resumed as pump can now flow enough - repeat

Edited March 26 by JohnMo

[Post and beam]

31 minutes ago, ProDave said:

When it switches to DHW it should completely ignore what it may or may not have been doing previously and get on with the job of heating the hot water. Anything else is a design fault.

As an untrained punter( and, the customer ) this is my view.

I repeat what i said previously. The boiler documentation says it can heat to 82 degrees if required. It should be able to give hot water for bathing in parallel.

[John Carroll]

1 hour ago, JohnMo said:

A quick read of the manual

 

The B is 

 

Fault category B (blocking faults)

Blocking faults result in the heating system being shut down temporarily.

The heating system restarts automatically as soon as the blocking fault is removed.

 

Not missing point at all.  It's a single boiler, that has a blocking code, this will prevent it firing up for any reason. The CH flow fault needs to be resolved with the flow through the boiler, otherwise it will only continue as it is.

 

Would suspect the following occurs

 

Trv's are open, boiler flows no issue, does heating and DHW as normal, trv's close in or fully closed, there is not enough flow through the system left open (2 rads and 15mm pipes), boiler gets blocking code. Boiler does fire for any reason while blocked.  Rooms cool, trv's open, heating resumed as pump can now flow enough - repeat

Even if the blocking code is up and assuming the boiler will/does c/o to HW then the pump can now flow enough through the PHEX, the blocking code should disappear very rapidly due to cold water on the other side of the PHEX, boiler fires up.

[Temp]

Does it ever lock out with just the CH running? Does it only lock out when you call for DHW or is that only when you notice it?

[Post and beam]

2 hours ago, Temp said:

Does it ever lock out with just the CH running?

I doubt i would ever be aware of it, dont even know how i could be aware of it. If the radiators were not receiving hot water for 4 minutes the effect would most likely be undetectable.

[John Carroll]

 

Has it ever cleared itself without you resetting it?, if not then it doesn't point to this 2965 fault which is self clearing.

 

I took some readings from someone with a WC 36CDI that had a fouled PHEX, it wasn't locking up but you might get some idea of the expected boiler flow temperature when it is producing HW.

 

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.

[Post and beam]

9 hours ago, John Carroll said:

Has it ever cleared itself without you resetting it?, if not then it doesn't point to this 2965 fault which is self clearing.

I have very definitely stated that it is blocking code 2965. And it does clear after about 4-5 minutes. There has never been an actual 'error' code on this boiler that would require a manual reset.

[John Carroll]

OK, if  this happen after using DHW constantly with no demand for CH in between (DHW demands) and if the boiler flow temperature is anywhere in the region I posted above during DHW demand then blocking code 2965 simply cannot be true which I would point out again to WB.

 

 If its coming up during a CH demand or CH anticycle or overrun then it will have to rise to whatever temperature it operates at, probably greater than 90C, unlikely, but possible, IMO. Again  just observe the flow temperature for the pump overrun time after switching off the CH demand and see what temperature it rises to.

Edited March 28 by John Carroll

[Post and beam]

7 hours ago, John Carroll said:

after using DHW constantly with no demand for CH in between

Not sure if 'after' is the condition we experience.  Most obvious and annoying is when we turn on the shower. It also happens when we open any hot tap in the house. The water remains cold.

So ' after using DHW constantly' does not fit our experience. Remember this is only every few weeks it might happen, it is not an everyday or every occasion condition.

I do not know what the actual flow temperature out of the tap is. i will measure it. It is set for 55 degrees.

[marshian]

52 minutes ago, Post and beam said:

Not sure if 'after' is the condition we experience.  Most obvious and annoying is when we turn on the shower. It also happens when we open any hot tap in the house. The water remains cold.

So ' after using DHW constantly' does not fit our experience. Remember this is only every few weeks it might happen, it is not an everyday or every occasion condition.

I do not know what the actual flow temperature out of the tap is. i will measure it. It is set for 55 degrees.

 

What is your flow temp for CH? I assume no weather comp (and you don't manually weather comp by changing flow temp depending on the weather)

[Post and beam]

Currently 76, was 82 through the winter because its a 1986 house.

[marshian]

2 minutes ago, Post and beam said:

Currently 76, was 82 through the winter because its a 1986 house.

 

I've just watched the video and seen that............. And agree with earlier comments that is bloody high for a CH flow temp - have you got tiny rads with no convector fins?

 

Mine is an 82 build house, std CWI and 100mm of loft insulation and 30 year old double glazing and even before improvements to the original rads 68 deg was more than enough CH flow temp for the 13 rads in the house only in a prolonged period of minus 5 did I raise it to 72.

 

82 is boiler flat out??

 

It's a condensing boiler and you are running it like an 80's non condensing boiler and at 80's efficiency levels - return temp must be 56 at best so only in the initial warm up phase (which will be bloody short) will it even condense.

 

[Post and beam]

2 minutes ago, marshian said:

have you got tiny rads with no convector fins?

No.

To be honest i think the boiler that it replaced 3 years ago, at 34 years old, heated the house better than this one. But until we build our new house this is what we have and it has the issues described.

[marshian]

1 minute ago, Post and beam said:

No.

To be honest i think the boiler that it replaced 3 years ago, at 34 years old, heated the house better than this one. But until we build our new house this is what we have and it has the issues described.

 

I don't want to be antagonistic here but have you attempted to see what the house actually needs flow temp wise for CH for a reasonable speed warm up and at a steady state?

 

Your old 34 year old boiler would have been fixed output, no modulation and minimal temp control - it would have also been chucking energy out of the flu. Yes they do heat houses quite well but are very inefficient compared to modern condensing boilers - I'd have a guess that you've seen little or no saving in terms of gas consumption since the new boiler was installed.

[John Carroll]

1 hour ago, Post and beam said:

Not sure if 'after' is the condition we experience.  Most obvious and annoying is when we turn on the shower. It also happens when we open any hot tap in the house. The water remains cold.

So ' after using DHW constantly' does not fit our experience. Remember this is only every few weeks it might happen, it is not an everyday or every occasion condition.

I do not know what the actual flow temperature out of the tap is. i will measure it. It is set for 55 degrees.

Yes, measure that temperature from the tap, the important one from a trouble shooting point of view is the boiler flow temperature which you should be able to access fairly easily from the menu, in DHW mode this temperature changes with the DHW demand, the DHW flow rate and temperature, and the mains temperature, unless the PHEX (plate heat exchanger) is very fouled then this should't remotely approach the blocking temperature, in any case if this was happening you would have noticed the shower/tap running hot and cold.

Edited March 28 by John Carroll

[Post and beam]

19 hours ago, marshian said:

I don't want to be antagonistic here but have you attempted to see what the house actually needs flow temp wise for CH for a reasonable speed warm up and at a steady state?

Of course. In the winter if it goes below zero then it needs to be 82 degrees. Funnily enough thats why i had it set at 82 Degrees.

 

Today 76 degrees is probably too much and i will be returning it to 70 until probably November.

 

John: i appreciate your efforts but i dont understand why the long sentence above. We have already discussed at length that Worcester Bosch cannot explain or fix the fact that in the winter months at least they cannot reliably deliver both CH and DHW without sometimes leaving us with cold water for washing. We know what is happening. They cannot fix it.

[JohnMo]

13 minutes ago, Post and beam said:

We know what is happening.

Told you that very early in the thread.  Obviously got shot down in flames by others, but more water volume needs to stay engaged - remove a couple more trv's or just open them to higher temperatures.

[Post and beam]

1 minute ago, JohnMo said:

Told you that very early in the thread

Agree

 

1 minute ago, JohnMo said:

remove a couple more trv's or just open them to higher temperatures

But that means us having to modify our chosen living conditions to suit an unsophisticated combi boiler. 

Mind you, i doubt Worcester Bosch are going to do anything about it so perhaps that is what i will have to do.  One thing is for certain, there wont be a combi in the new build.

[John Carroll]

Its truly amazing that WB havn't divulged (or have they?) what temperature that code 2965 operates at as in my IMO its the key to the whole discussion/argument, if it operates at say 88C then because you can "legally" set the flow temperature to 82C and the burner won't trip until the flow temp reaches 87C/88C then clearly a WB problem but if it operates at say 95C then its a circulation problem (for whatever reason) when the boiler goes to either recycle or pump overrun to cool the boiler HEX, then not a WB problem.

Maybe a clue in this whatever possible means.

Edited March 29 by John Carroll

[marshian]

1 hour ago, Post and beam said:

Of course. In the winter if it goes below zero then it needs to be 82 degrees. Funnily enough thats why i had it set at 82 Degrees.

 

Today 76 degrees is probably too much and i will be returning it to 70 until probably November.

 

I'm frankly amazed that any house needs 82 deg flow temp for rads - your heat loss must be horrific

 

Even 70 is high for spring, summer and autumn - the boiler is barely into condensing mode.

 

Does the HW issue occur when you are running at 70 deg flow temp for the CH in spring/autumn

 

I'm currently running radiator flow temp at 55 today I only need maybe 2 hrs of heating this evening - I could run it longer at lower temps but 55 gets the house up to temp a little quicker.

[JohnMo]

41 minutes ago, Post and beam said:

modify our chosen living conditions to suit an unsophisticated combi boiler.

Nothing unsophisticated, just simple science, if you throw lots of kW of heat at water it will overheat, unless it's moved at a fast enough rate to carry the heat away. You are basically trying to heat up everything too quickly, the trv's shut off the radiators they kill the flow route. You get the blocking alarm. No heating no DHW until  lock is released.

 

You would have the same issues with any heating device, even bigger issues with a heat pump.

 

The alarm you get is just a low flow alarm and it locks the boiler until resolved.

 

Our last house was 200 years old most uninsulated thick stone walls and single glazing. We never ran the boiler over 60.  The only time I had issues, was when I added timers and electric trv's to the radiators. Undid what I did, never had an issue again.

 

Run a cooler temperature for longer, will fix nearly all your issues.

[SteamyTea]

1 hour ago, marshian said:

I'm frankly amazed that any house needs 82 deg flow temp for rads - your heat loss must be horrific

Or the radiators are the wrong size.