Issues with new heating zone

K.Flyer · 02-12-2019 01:16PM

What settings have you got your valves at?
If they are too low they could be shutting down too soon and not satisfying zone heat requirements.
Turn them up full for a while and compare results.
Sometimes you get a little bit of black water. But if draining a 500ml sample shows water quite dark / black your system is contaminated and should be cleaned out and treated for better efficiency.

powerade · 02-12-2019 05:47PM

All of the TRV's are set at 5 with the exception of the hall and one bedroom radiator which are turned off and one bedroom radiator is set at 3. The TRV'S in the two rooms with the digital thermostats are always fully open. Zone 1 will not cycle, to the best of my knowledge, if all of the TRV's are fully open. Zone 2 appears to cycle regardless as to whether all of the TRV's are fully open. At the risk of asking a stupid question, what is happening when the boiler cycles and what triggers it? The temperature rises to between 69 and 71 degrees so something must be driving it up. Something then kicks in to lower the temperature but I would expect it to drop and settle around 65 degrees. That's not the case, however, and I have seen it drop to as low as 28 degrees. Thank you so much for your help with this.

John.G · 02-12-2019 08:04PM

How long does it take the temperature to fall to - 28C before boiler fires up again?...can you time it please.o

powerade · 02-12-2019 08:33PM

That degree of fall off is not the norm and I don't know how I can replicate it. From memory, however, I would say no more than 2 to 3 minutes.

John.G · 02-12-2019 08:49PM

I don't know the anti cycling logic of that particular boiler but I think 5 mins off time might be reasonable to assume, one would then expect the boiler to fire up and increase it's temperature to - 75c before cut or and another 5 min off time, IF this is the case then one would not expect the temperature to fall to 28c in 5 minutes except that the boiler is not reaching 75c each time it re fires.

powerade · 02-12-2019 09:29PM

Thank you for your post.The temperature never reaches 75 degrees, the normal maximum is 69 to 71 degrees. The boiler is set at 65 degrees and I think that the standard cycle is +- 5 degrees, based on an earlier post. I have spoken to Worcester Bosch and they do not believe that it should be cycling, I.e. it should be purring along at 65 degrees. Instead it is up and down and the constant noise from the boiler is ridiculous. Plus the heating is inefficient and impractical in Zone 2. So, what I would like to understand is why it is cycling and what needs to be done to stop it cycling.

John.G · 02-12-2019 10:26PM

It will only purr along at - 65c if it's maximum turndown is greater thanks the radiator output, if the radiators emit 5 kw and the boiler minum output is 6 kw the it has to cycle, period. Remember a oil fired boiler has a fixed output my own 20kw boiler might cycle 2 min on 4 min off when the cylinder coil demand might be only 2kw when the cylinder is nearly up to temperature.

You could shut off say 2 rads in zone1 which will force the boiler to cycle with just this zone1 on and see if you have the same problems.

powerade · 03-12-2019 09:58AM

Thanks John. So, if I have understood you correctly, if the combined output of the radiators is less than the minimum output of the boiler, it will cycle. It was interesting that you mentioned your oil fired boiler asI had noticed that my Dad's boiler was constantly coming on and off but it didn't appear to impact the heat of the radiators. So, in my case, if I have all of my radiators on and all of the TRV's open it should be unlikely for the boiler to cycle. If I turn radiators off and/or lower the TRV settings, I am reducing the radiator KW output and the boiler is likely to start cycling, at some point. Am I on the right track as that makes sense to me in the context of what I have observed. I will run a few more tests today.

Given that Zone 2 is smaller in terms of KW output than Zone 1, I can now understand why it is cycling after around 15/20 minutes. Can I just ask a few more questions on this, if I may:
1. Is the boiler output fixed or variable (WB 25i Greenstar Combi)
2. There is a TRV on the radiator in the room with the digital thermostat in Zone 2. The TRV is always open but I am wondering if it might close the valve to the radiator which might help to explain why this room is taking so long to heat up
3. How can I tell if the boiler is cycling as expected, e.g. the temperature drops to anything less than 60 degrees which is outside of the minus 5 degree range. Thanks again for your help

powerade · 03-12-2019 10:29AM

John.G. I just watched the boiler cycle with only Zone 1 on. At 9:16 the temperature rose to 70 degrees. It then fell rapidly to 59 degrees. By 9:20 it had fallen to 51 ddegrees. The boiler then fired up, the temperature rose rapidly to 62 and then back down to 60 (9:21). It is now 9:28 and the boiler is settled at 65 degrees, for now.

John.G · 03-12-2019 12:08PM

The reason that it has settled down is because the radiator output or demand is higher than the minimum output of the boiler if you now shut down say 2 rads in zone1 then the boiler should cycle.
Z take some readings then over a number of cycles.

Yes the heating output of the boiler can be reduced without affecting the heat output to hot water (showering etc) and it
May help but even though the output may be reduced (range rating) the min output will still remain the same, for example if you reduced the output from say 24kw to 10kw then the minimum output will remain unchanged so you can still get cycling. I don't have domestic gas boiler experience but you may be able to access this function from a user accessible menu. Someone on here may be able to assist.

03-12-2019 12:11PM

Try removing a TRV head off one of the rads on zone 2.

Dtp1979 · 03-12-2019 01:12PM

Still sounds like dirt to me and possibly the rads are undersized upstairs

powerade · 03-12-2019 01:34PM

Cheers John. If it is dirt in the system, do I just need to get the system flushed? I replaced all of the radiators in the house when I moved in 7 years ago and the plumber re-assessed the BTU when the combi boiler was installed three years ago so I think I should be ok on radiator size but worth checking again.

John.G · 03-12-2019 02:44PM

I didn't suggest dirt in the system did you shut off
Two rads more in zone 1 to get the boiler to cycles and take Agee readings for a few cycles + times off and on

03-12-2019 03:49PM

Let’s keep this simple as I’m a simple man.

Remove the heads of the trvs on zone 2 to see how things work with no mechanical restrictions, if you find the boiler is still short cycling you than have to determine why, so you get somebody in to look at your pipework and controls.

If you find it works then refit all the valves bar 1 which can be called your bypass rad, if you find this works for you then have your auto bypass checked or leave the valve off.

John.G · 03-12-2019 04:57PM

Gary, surely a gas boiler can cycle and still supply a reasonable flow & return temp just like a vokera vision 20S that I think I mentioned previously, there seems to be some percularity about this particular boiler's cycle/anti cycling that we migjht e able to fathom out, one shouldn't have to make your system fit the boiler.

powerade · 03-12-2019 05:46PM

I returned off two radiators in Zone 1 and the boiler cycled almist immediately. It took 4 minutes for the boiler to fire up and then the temperature climbed rapidly to 71 degrees and then straight back down to 60. It appears to be cycling every 4/5 minutes and it has not settled at any point at 65 degrees. (16:21, 16:26 and 16:31)Also, it has consumed 1/2 unit of gas to heat 2 radiators in 30 minutes. That is comparable with the consumption to heat the whole house in the same time period.
I would love to keep this simple Gary but I have a feeling that there are a few contributing factors. The zoning work was only completed in May of this year and the plumber who installed the pipework and controls is adamant that everything is working as expected. If I don't have some kind of handle on the issues, I could waste an awful.lot of time and money on another plumber. So, I am extremely grateful for everyone's input and advice.
It would appear that the boiler is cycling, as John suggested, because the combined radiator output is less than the boiler minimum output and that would explain why the cycling has only become an issue after the heating was spilt into two zones. Prior to that I would have been running most of the radiators in the house.
I am going to leave Zone 2 off today. Tomorrow I will remove the TRV head from the radiator in the room with the digital thermostat and I will monitor the temperature in this room and the bedroom in Zone 2 to see if the two rooms are heating at the same rate.
With the two radiators back on in Zone 1 now, the boiler is purring along at 65 degrees and it sounds a lot less labored than it did with just the two radiators on . It will cycle but I think it was taking about 30 minutes yesterday for it to cycle with four radiators on compared to the 4/5 minutes with just two radiators on.

03-12-2019 06:04PM

John.G wrote: »

Gary, surely a gas boiler can cycle and still supply a reasonable flow & return temp just like a vokera vision 20S that I think I mentioned previously, there seems to be some percularity about this particular boiler's cycle/anti cycling that we migjht e able to fathom out, one shouldn't have to make your system fit the boiler.

I like to start at the beginning and work from there.

You can’t put a elephant in to a rabbit hutch:cool:

If the boiler is set for whole house heat and hot water requirement which you then push in to a circuit that has a alternating mechanical restriction then it’s not unusual to see what the op has on a small circuit, a bypass rad would be required on every zone with trvs or a very good auto bypass before the zone valves but before I do anything I would want to prove to myself that the zone works.

I Am The Law · 03-12-2019 06:48PM

Can you confirm that the Flow from and Return to the boiler have not been swapped by mistake when first installed?

powerade · 03-12-2019 09:45PM

How would I check that?

I Am The Law · 03-12-2019 10:12PM

powerade wrote: »

How would I check that?

You could check the boiler installation manual, then compare it to the direction arrow on the circulating pump.

powerade · 03-12-2019 10:15PM

Gary, is a bypass radiator one that does not have a TRV? The by pass valve is just above the two zone valves and it is set at 0.1 (max setting is 0.5). I get what you are saying about fitting an elephant into a rabbit hutch but I would have thought that it is quite common to split a house into multiple heating zones these days and that my boiler should be able to cope with a reduced KW demand from the radiators.
When you say that you would want to see if Zone 2 is working, I don't quite follow what you mean by that. It comes on, the boiler cycles like mad and it takes forever to heat up. So it behaves differently to Zone 1 but it still works. By working do you mean that the boiler does not cycle and it heats in in a comparable time to Zone 1? I will happily remove all of the TRV's and test the system as you suggest but I just want to know what I should be looking for.
In my view, the system should be configured to prevent cycling and to deliver constant heat to the radiators, when the demand is there but I don't know, at this stage, if that is actually possible.

John.G · 03-12-2019 10:59PM

I didn't realise that you had a ABV set o 0.1 which is 1 meter, absolutely crazy, set this now to say 0.3 and see how you get on.

powerade · 03-12-2019 11:08PM

Is that setting supposed to represent the distance from the boiler to the ABV?

John.G · 03-12-2019 11:17PM

No, it's set so to keep a minum flow through the noiler as zone valves close in.. I will explain it tomorrow but for the moment just close to a setting of 0.3/0.35 z

powerade · 03-12-2019 11:21PM

Will do

03-12-2019 11:46PM

powerade wrote: »

Gary, is a bypass radiator one that does not have a TRV?

Yep.

powerade wrote: »

The by pass valve is just above the two zone valves and it is set at 0.1 (max setting is 0.5).

I don’t trust anyone or anything till I test it, just because it’s there doesn’t mean it’s having a positive impact.

powerade wrote: »

I get what you are saying about fitting an elephant into a rabbit hutch but I would have thought that it is quite common to split a house into multiple heating zones these days and that my boiler should be able to cope with a reduced KW demand from the radiators.

it’s not just reduced demand it’s also movement, you are creating a higher restriction on the boiler circuit by running fewer rads.

powerade wrote: »

When you say that you would want to see if Zone 2 is working, I don't quite follow what you mean by that It comes on, the boiler cycles like mad and it takes forever to heat up.

as above your putting restrictions on the circuit, I would want to prove everything works correctly first before I restrict the circuit, this can help determine a plumbing issue or boiler issue.

powerade wrote: »

So it behaves differently to Zone 1 but it still works. By working do you mean that the boiler does not cycle and it heats in in a comparable time to Zone 1? I will happily remove all of the TRV's and test the system as you suggest but I just want to know what I should be looking for.

you should see less cycling which should allow the rads to achieve temperature quicker as the boiler stays on longer.

powerade wrote: »

In my view, the system should be configured to prevent cycling and to deliver constant heat to the radiators, when the demand is there but I don't know, at this stage, if that is actually possible.

It is possible but it’s a balance between keeping up the movement of the system without allowing the bypass rad or auto bypass allowing the flow from the boiler to ignore the rads altogether.

powerade · 03-12-2019 11:52PM

Thank you Gary for such a comprehensive response. So I should remove all of the TRV's on the radiators in Zone 2 and see what happens. I will also set the ABV to 0.3.

John.G · 04-12-2019 11:21AM

Reset the ABV to ~ 0.35 first as the 0.1 (1M) setting will only result in the water short circuiting the rads and is probably the main culprit in your problems and whoever installed it IMO must have set it low as I think the setting is preset to 0.3 bar or 3M.
Google Honeywell DU145 to get a feel for the setting, Iwould imagine that your circ pump is running on the highest speed setting since it's a combi.

powerade · 04-12-2019 02:45PM

I set the ABV to .35 this morning and turned on Zone 1. It still cycled as before but it appeared to take significantly longer for the temperature to move from 65 to 69 degrees before commencing the downward descent. In 30 minutes the Zone 1 temperature increased by 2.6 degrees. I then turned Zone 1 off and turned on Zone 2. In 30 minutes the temperature increased by 1 degree in Zone 2. It is still cycling with the temperature climbing as high as 71 degrees. The interval between cycles in not consistent and is anything from 2 to 15 minutes. The radiators feel warm but they are not belting out heat.
So, it would appear that changing the setting on the ABV has not had an impact on the cycling in Zone 1. It is a small zone with one large double radiator, two large single radiators and a towel rail in the en-suite. One of the large single radiators is permanently turned off.
If I remove all of the TRV heads, are they easy enough to re-fit?

Issues with new heating zone

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