Issues with new heating zone

So whats the issue with the system?

powerade wrote: »

My heating was spilt into two zones in May of this year. Over the last few months I noticed that Zone 2 was much slower to heat up than Zone 1 when both zones were on together and Zone 2 was taking hours to heat up when it was running on its own. Zone 2 constantly stop/starts when it is running on its own and it would appear that this is a contributing factor to the slowness of the temperature rise in Zone 2, when just that Zone is running. It is unclear as to what is causing the difference in the rate of temperature rise between zone 1 and 2 when they are both running together as the boiler does not appear to stop/start. It has been suggested that there might be dirt in the system. At the moment we are trying to determine the impact of the AB
V setting and TRVs on the heating up of the radiators and it would appear that the radiators get significantly hotter in both zones when the ABV is closed. This marginally improves the rate of temperature rise in Zone 2, when both zones are running. Zone 1 will usually get to temperature on an hour or less but Zone 2 will not. Therefore it will continue to run on its own at which point the stop/start kicks in and the rate of temperature change reduces considerably, e.g. 30 minutes to rise by .2 degree. I think that sums it up

I think its no harm to add that when you ran zone1 on its own and shut off 2 rads (only 3 "on line") the boiler was cycling as one would expect with a off anti cycle time of 5 mins but the cycling time/temps when cycling on zone2 were inconsistent?.

So now that the ABV is closed have you established if zone2 (with zone1 off) rads are "roasting" and what is happening with anti cycle times/boiler temperatures when the boiler starts to cycle as per normal.

powerade wrote: »

John, see post number 118. Now that I can use the info function on the boiler I can see that when the temperature reaches 69 degrees (Zone 2 on) the pilot light will stsy on but the status changes to "System Waiting". It will stay on this status for around 4 minutes. The status then changes to "System heating up" the temperature soars to 70 degrees and the status changes again to "System waiting". This will last another 4 minutes and then the status will change to "anti rapid cycle" which lasts for about 2 minutes. Then the heating comes back on. This cycle was repeated after 15 minutes and I saw it happening with Zone 1 the other day. I need to run the two zones together again to for a bit longer, as suggested by right job

To my simple way of thinking if you only need say 2 or 3 kw of rad output then this boiler does some strange things which I will post later, to me this is absolutely crazy, as I said previously a oil fired boiler which runs flat out can easily supply around 2 kw even if does cycle like mad. More later.

This is from the e manual or your own hard copy:

"Table 33, System Waiting; Primary flow temperature above temperature set point.

Anti rapid cycle mode. • The boiler has commenced anti-cycle period for CH. Can be adjusted in boiler settings (2.3b). • Default 5 Minutes


Apoligies: Anti fast cycle should have been anti rapid cycling so no connection to hot water demand


Did the off time exceed 5 minutes?, you mentioned that this cycle was repeated after 15 minutes and what was the boiler flow temperature at its lowest point?.

Thanks but did you notice what the lowest boiler flow temperature was during all these periods.

Increasing the boiler set point will certainly increase the rad output.

Powerade, what evidence have you got that the boiler return temperature is > the flow temperature.

The displayed temperature is the FLOW temperature.I must look at the e manual in a minute but I don't think you can even see the return temperature in the menu tables.
Will get back re radiator temperatures.

Yes, the only measured/displayed CH temperature is the Flow.

Re radiator temperatures. radiator outputs are now based on a "50 deg" rating which is the mean radiator temperature minus the required room temp, 20C is generally used. so if you had a radiator with a flow temp of 75c and a return temp of 60C, the mean is 67.5C, 67.5-20 = 47.5c so you have a "47.5C" rad which will emit (47.5/50)^1.3 or 94% of a 50 deg rad and so on. Now you have a flow temp of 65c and assuming a return temp of 50 then you have a ((65+50)/2)-20, a 37.5 deg rad which will only emit 68% of its 50 deg rated output, if you now increase the flow temp to 75c you will get (as shown above) 94% output of a 50 deg rad but you will get a increase of ~ 38% over your present 65C flow temp. That should satisfy your zone2 problems or you could just increase it to 70c as a interm measure and see how you get on. we can look at the condensing effects later on, if you have a infra red scanner it would be very helpful in establishing the return (and flow) temps for comparison.

The flow pipe is the "leftmost" pipe coming out of the bottom of the boiler and the return is the "rightmost" pipe returning to the boiler, I think, items 2.2 and 2.6 in your manual. You might just feel them with your hand tc confirm that they have been connected in properly first day and also you can get a very rough idea of the temperature difference between them.

I would just increase it to 70C now and see what happens.

It may make a difference when both zones are opened but if they are uniformly hot then ??.

Have you noticed/tested on zone2 only when it starts to cycle, make a note of various times etc and most importantly of all note the minimum temperature during a couple of cycles, if the minimum is not less than 63/65C (with a setpoint of 75C) then that is fine and is just as "good" as a constantly cycling oil fired boiler which has a boilerstat hysteresis of 10/12C.

re that heat scanner you've got, is that jumping around if measuring say the ambient temp or if you take cover off a boiling kettle does it give a steady measurement?, if so you might put a bit of black insulation tape on any pipe you want to measure and point the gun at this, it would also be useful for getting a comparison between the flow/return on each rad.

If the boiler was firing at full output for 65 minutes then it would point to the rads emitting ~ 20 kw which seems very improbable as it only takes ~ 4.5 kwh to heat the water contents of say 75 litres from 20 to 70C, my own 20 kw boiler only takes 20/25 minutes from cold to heat up from 20 to 75c with all zones on so I would think that your boiler was not firing at full output for this period, more like 12/15 kw.

I can only suggest for the moment that you carefully note down the system waiting time, water heating time etc and the temperatures.

What is the max output range rated to? you looked at that you said in another post.You could also range rate (max output) down to 12kw just to see what affect this has because all the posts that I have read seem to suggest that a partial solution, at least, is to de rate the boiler down to match the installed radiator outputs.

Edit: The boiler more than likely DID modulate down after x minutes and it was only when the rad demand was lower than the boiler minimum output that it cut out after 65 minutes.
Altough it is very difficult to see how this occurred if both zones were still calling for heat and the rads were only outputting < 7 kw.