Advice needed regarding weather comp for Vaillant 637

[V1ks]

Hey Guys...

 

I have the below setup currently and need your advise if installing weather comp will provide me better way to get the most efficiency out of my oversized boiler. its a long story reg why this big boiler was installed as at the time of install i had no idea about sizes etc and it was all done by the stupid plumber who did he whole thing. Now im just trying to get the most out of the setup i have.

 

Vaillant 637 system boiler with Horizontal unvented tank 210L. - both are in the loft eves. I have Hive system for controlling the Rads and using Heatmiser Neo for the UFH. 

 

I have ground floor (kitchen 30 sqm and living room 24sqm) which is running on UFH. 1st floor (3 rooms) + Loft room has Rads installed along with towel rails in the 2 bathrooms. 

 

UFH heating works fine no issues on that part apart from the fact that i need to run it at slightly higher temp than i want to (50c at manifold TRV). Boiler flow is set to 65C at present. 

 

My issue:

 

1 - if i run the kitchen UFH alone (its a single zone) - then the boiler hits the desired temp and then goes into the egg timer screen (Anti cycle i believe). and keeps doing this - i assume this is because my boiler is too big

2 - If the kitchen and living room UFH is on together then i dont face the anticycle issue and boiler would be sitting at the target flow temp just going up and down 1c (if i rem correctly). 

3 - I have hive TRV's on the 4 rads (in each room) and generally only need to warm up 3 rooms - when running just the rads i get the anticycle mode.

 

From my above issues I know my boiler is too big for my house and for the setup i have, i know i can change the settings to reduce the kw it runs at but im not sure if that's a good way? Would installing Weather Comp would help me in my current situation. Im just trying to get the best out of what i have, or if i can install anything else to make this better. 

 

I had the boiler serviced recently and during that visit i asked the engineer if he thought my system was not setup correctly and i asked if the boiler was too big >> his response was "everything is running as it should and its good to have a bigger boiler" >>so i didnt even bother asking about weather comp to him.  Hence i've come here as there are a lot of you guys who seems to know hell a lot more than some of the pros. 

 

Happy to provide more info, if i have missed anything. 

 

 

[JohnMo]

Running weather comp will not help if you leave your system full of thermostats , the zone size is what is causing the issue, as you describe yourself, kitchen only, an issue, kitchen and living room on together no issue etc.

 

You may be better merging the UFH so it acts as one zone, i.e. drive the loops from a single thermostat. The same with the radiators.  So you have only a couple of zones.  You will need to balance the system flows afterwards, to get an even output from the loops and radiators.

 

By the way your plumber is speaking nonsense.

 

If you are plumbed as an S or Y plan, you will not be able to run weather compensation, as it will reduce the cylinder reheat temperature also.

[V1ks]

22 hours ago, JohnMo said:

Running weather comp will not help if you leave your system full of thermostats , the zone size is what is causing the issue, as you describe yourself, kitchen only, an issue, kitchen and living room on together no issue etc.

 

You may be better merging the UFH so it acts as one zone, i.e. drive the loops from a single thermostat. The same with the radiators.  So you have only a couple of zones.  You will need to balance the system flows afterwards, to get an even output from the loops and radiators.

 

By the way your plumber is speaking nonsense.

 

If you are plumbed as an S or Y plan, you will not be able to run weather compensation, as it will reduce the cylinder reheat temperature also.

 

Thanks for replying back, yes i have thought about just having 1 thermostat for Kitchen and living room to stop the cycling so i can explore this option for sure. The only thing id have to fig out is the new location for the single thermostat as my living room and kitchen is separated by internal folding doors (wood/glass). In the winter the kitchen does get more colder compare to living room, so if i had 1 stat controlling both would it not be an issue as my living room would just keep getting warm until the kitchen reached the target temp (assuming i keep the single thermostat in the kitchen). And if i kept it in the living room it could be that kitchen stays cooler as living room is likely to warm up faster. Its for this reason ive kept 2 stats one for each area. 

 

Regarding the S or Y plan - I believe (correct me if im wrong) i have a S plan as i can see that we have 3 Motorized zone valves >> one for heating, one for cylinder and the other for UFH. It 

 

 

Edited May 11, 2023 by V1ks

[JohnMo]

For the kitchen living room, use the coldest room as reference or even the hallway, then balance the UFH flow rates.  To make a room heat up more, you increase flow rate at the manifold, by adjusting the flow meters (say 0.5 l/min at a time) for the loop or loops in that room, to decrease the heat output you decrease the flow rates. Do a small amount each day.

[Lofty718]

I've got a Vaillant 630 with weather comp, in winter my boiler runs around 40c I am able to run two different flow temperatures for heating (ufh and rads) and then a seperate temperature for the cylinder on hot water priority

 

I run ufh at 30-35 flow temp and rads not much higher, obviously it depends on outdoor temps. The sensocomfort vrc720 and vr71 are very good.

 

How long a burn time do you get before the boiler goes in anticycle mode? with my 630 I get about a 15minute burn time and the boiler is very oversized maybe double so I"ve range rated it down to 15kw.

 

 Mixing valve on the manifold is a no no and old tech. Underfloor heating should be controlled by an electronic mixing valve like an esbe with an actuator.

 

 

[V1ks]

On 11/05/2023 at 12:32, JohnMo said:

For the kitchen living room, use the coldest room as reference or even the hallway, then balance the UFH flow rates.  To make a room heat up more, you increase flow rate at the manifold, by adjusting the flow meters (say 0.5 l/min at a time) for the loop or loops in that room, to decrease the heat output you decrease the flow rates. Do a small amount each day.

Thanks ill give this a try in the winter now and see how things go...

 

On 12/05/2023 at 00:34, Lofty718 said:

I've got a Vaillant 630 with weather comp, in winter my boiler runs around 40c I am able to run two different flow temperatures for heating (ufh and rads) and then a seperate temperature for the cylinder on hot water priority

 

I run ufh at 30-35 flow temp and rads not much higher, obviously it depends on outdoor temps. The sensocomfort vrc720 and vr71 are very good.

 

How long a burn time do you get before the boiler goes in anticycle mode? with my 630 I get about a 15minute burn time and the boiler is very oversized maybe double so I"ve range rated it down to 15kw.

 

 Mixing valve on the manifold is a no no and old tech. Underfloor heating should be controlled by an electronic mixing valve like an esbe with an actuator.

 

 

 

I haven't really timed the burn time before it goes into anticycle mode but if from memory the chain of events are: 1. Kitchen alone calls for heat and boiler would fire up, it would then get to say 65c and then hit the anticycle mode for the time set and then it would sit on this for about 5-7min and then start up again...

 

I did range rate it down to 12kw at one point but i dont think it run it for long enough to test, so i may try that again once i have figured what is the lowest kw i can go to. 

 

Sorry what do i mean by the below, as my manifold has the manual valve to set the temp for the flow water and electronic actuators>> isn't this normal.

 

"Mixing valve on the manifold is a no no and old tech. Underfloor heating should be controlled by an electronic mixing valve like an esbe with an actuator."