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That is very clever.

But hopefully the cylinder heat up will be accomplished before the +5C point. Boiler stat turned up a touch - I'll see what happens tomorrow. (I use a paper ring that I have printed with divisions at every 7.5° so that I can roughly track the settings that I use. The 24ri has a range of approx...

That's very interesting. How did you determine the coil heat input?

@Johntheo5 Thank you for that - you have prompted a 'lightbulb moment'! Looking back at my last temperature plot the flow temp is fairly flat and steady at ~67-69C for probably about 20 minutes after the initial heat up and then has a little 7 minute 'burst' up to 73C when it then shuts off. Is...

In the last plot, water was heated for a one hour cycle from around 09:00 to 10:00 - (much later than usual so that I could measure return temps) - so still adequate hot water after 8 hours. Our hot water usage is fairly low - there are only two of us so showers and a couple of washing up...

Attached is today's plot of flow and return temps. There is some interpolated data as you will see but nothing that significant. Max dt in the period for which I have actual measured data is ~7C. When you look at the plots please bear in mind that the flow temps will be fairly accurate but the...

Probably! And I agree with your comments about the tank stat accuracy. Yes, it does. Agreed. I will be asking them to define this next week.

The engineer who came a couple of weeks ago didn't know what temperature reduction to expect before re-ignition! He phoned back to base and was told '3 minutes (i.e. pump overrun time) plus 6C'. In my case the system never shuts off, of course, so I don't know if this has any relevance. However...

Attached is this morning's plot of return temperature. I haven't superimposed this on any of the recent flow temperature plots as the starting temeprature in the cylinder would be different. However, the shape of the curve is identical to the flow plots and, guessing, maybe initially within...

All re-wired and zone valves on HW and CH circuits so no chance of water heating unless demanded by time clock.

That was a suggestion from the last WB engineer. Something definitely worth looking at. But @DP said in an earlier post ...... ....... so do you think that it will work? And flow or return? (Pump is on the return.)

Totally bonkers! And yes, the engineer who replaced the PCB was in a rush to get off so didn't wait to monitor a full HW cycle. Second engineer spent more time looking at the system and relaced the thermistor 'just in case'. Cylinder is fully insulated (as supplied) so minimal heat loss...

I think that you are probably right. Much of my working years were spent in the technical ceramics industry where precise temperature control of our kilns was imperative. I well remember the vagaries of PID control although after many years of retirement I've forgotten most of it! I'm heading...

When I do measure / log the return temp I am expecting to see it equalise with the flow after that initial heating period of ~30 minutes followed by a very slow fall. Yes, I agree, there should not be a reduction of 18C before re-ignition.

Did that earlier today just to double check.

The pump is on the return and pumping in to the boiler. Flow is to the top of the HW coil and return at the bottom which is correct. The last WB engineer queried the pump location but in my (limited) experience it is quite normal. In any event, I doubt that it would have any bearing on my...

May have to delay return temps until Thursday. Flow temps were definitely not right this morning - spot check showed return higher than flow! Temp probe may not have been located properly under the pipe insulation so I want to re-check tomorrow. I have had an 'on-line' chat with WB this...

Something odd about today's data from the temperature logger - actual recorded figures do not look right (too low). Even so, the performance was still similar with pump speed at 'II' - large temperature drop and ~20 minutes before boiler re-fired. I will repeat tomrrow. However, HW heating shut...

Thanks for the useful comment. My plan is: Pump speed set to the 'II' position. (This hasn't made any difference to the CH this evening.) Tomorrow I will monitor the flow temperature again and see if anything has changed. Wednesday I will monitor the return temperature and compare to the flow...

Yes, it is. The old Halstead boiler was gravity feed. This was commented on by the Bosch engineer who came out last Saturday but he didn't say that it was a 'no, no'. He did suggest that restricting the flow on the HW circuit might be effective.