Underfloor heating not working correctly

[kenjiru]

I've bought an old house and converted it from radiator heating to underfloor heating. I've reused the old gas boiler Vaillant ecoCOMPACT VSC 206/4-5 90 that had an multiMATIC 700 module already installed.

Heating work fine for the first floor, but it does not work correctly for the upper floor, the temperature there reaches a maximum of 18 C. I suspect there is problem with the design of the system, as it was done by a plumber that I don't trust very much now.. The elevation for the second floor is approximately 5m from the boiler in the basement.

Before hiring a proper heating company (that I don't know and trust) which also probably cost a lot, I would like some opinions on the design of the heating system.
I've attached a couple of pictures with the installation, please let me know if you need more information.

 

[SimonG]

Why don't you trust your plumber?

Nothing in them pics to give any idea of heating design.

Heating designs cost money, I don't do them for free.

 

[Gasmk1]

yes we do mixing valves pumps for heating ?

 

[SJB060685]

As above where are the blending valves and pumps for each manifold?
Did your plumber adjust flow rates and properly commission?
Are they on separate zones etc etc?

 

[kenjiru]

First of all I want to mention that I have no prior experience with heating systems. I've always lived in some kind of apartment where I didn't have to worry about these issues.

My Vaillant gas boiler is configured to provide a temperature of ~ 40 °C depending on the temperature reported by the outside sensor. For this is using this heating curve setting, that is set to 0.35 right now.

After running into this issue with the heating, I did a bit of research myself and noticed that a lot of people use manifolds with pumps and blending valves. But this setup is used when their boiler can't provide the lower temperature required by underfloor heating. Or when they have both radiators and underfloor heating circuits in the same house. Here in Austria, all the people I've asked have heat pumps or gas boilers that provide a constant low temperature and their manifolds don't have any pumps or valves.

Anyway, I'm still surprised how the plumber did that split for the 2 heating circuits for the separate floors. I was expecting a more elaborate solution. I expect that most of the water will go through the circuit for the ground floor instead of the second circuit that climbs the 5m to the second floor.. This is where I would like an advice..

 

[SJB060685]

Hi from England. First I just want to point out I'm not an expert in this field, I'm still studying it but I'll see if I can shed some light.

First do you have one module controlling both circuits? I've had a look at manual and there should be one per zone.
Two. What is the curve set to and temperatures outside at the moment?
What's the buildings insulation levels like? A well insulated building will require a lower heat curve and vice versa for a poorly insulated dwelling.

 

[SimonG]

So the circuits have no pumps.

Well theres the problem.

 

[SJB060685]

So the circuits have no pumps.

Well theres the problem.

I think hes implying just the boiler pump, which I suspect is struggling to cope but I've asked a couple other questions as well

 

[Chuck]

This looks to me like a system that was designed for a low temperature heat source, i.e. your 40°C flow so no need for a blending valve and separate circulating pump for the UFH.

The obvious problem is someone has taken all the actuators off the upstairs zone valves so they are fully open all the time and this may be the problem with the downstairs zone: upstairs is scoffing all the heat. You can even see a dangerous looking piece of cable, which should probably be connected to a missing control box.

The actuators on the downstairs zone are all present and so is a control box.

So, I think you will need someone competent to review the system, reinstall the missing components and recommission the controls. You may need a couple of balancing valves installed to get the correct share going to each floor, but if the controls are sufficiently good this may not be needed.

It's possible that the section where the split is made (the last photo) has been plumbed incorrectly. There are two gate valves that would act as balancing valves if they were on the other side of the branch and the colour coding of the insulation looks incorrect to me.

I wouldn't recommend this as a DIY exercise for most people as fixing systems that have never worked correctly can be quite tricky and benefits greatly from experience.

 

[SJB060685]

This looks to me like a system that was designed for a low temperature heat source, i.e. your 40°C flow so no need for a blending valve and separate circulating pump for the UFH.

The obvious problem is someone has taken all the actuators off the upstairs zone valves so they are fully open all the time and this may be the problem with the downstairs zone: upstairs is scoffing all the heat. You can even see a dangerous looking piece of cable, which should probably be connected to a missing control box.

The actuators on the downstairs zone are all present and so is a control box.

So, I think you will need someone competent to review the system, reinstall the missing components and recommission the controls. You may need a couple of balancing valves installed to get the correct share going to each floor, but if the controls are sufficiently good this may not be needed.

It's possible that the section where the split is made (the last photo) has been plumbed incorrectly. There are two gate valves that would act as balancing valves if they were on the other side of the branch and the colour coding of the insulation looks incorrect to me.

I wouldn't recommend this as a DIY exercise for most people as fixing systems that have never worked correctly can be quite tricky and benefits greatly from experience.

I had noticed the actuator heads were all missing on upstairs loops like you said, however he says the problem lies with the upstairs? Which is why I assume he has taken actuators off and fiddled weather compensator curves?
Could this not be a pump problem? If he's relying on just the boiler pump I'd imagine it doesn't have the guts to supply upstairs?

 

[Chuck]

I had noticed the actuator heads were all missing on upstairs loops like you said, however he says the problem lies with the upstairs? Which is why I assume he has taken actuators off and fiddled weather compensator curves?

Good catch, I misread the description of what was going on thought that it was downstairs that was cold.

Could this not be a pump problem? If he's relying on just the boiler pump I'd imagine it doesn't have the guts to supply upstairs?

It's certainly a possibility. But, on a system that has never worked properly, everything is a possibility including: incorrect pipework, valves left closed, airlocks, not enough water in the system, etc...

 

[kenjiru]

First do you have one module controlling both circuits? I've had a look at manual and there should be one per zone.

From what I've read, the gas boiler alone can control only one heating circuit. There are expansion sets that enable it to control additional circuits, but I did not look very close in this direction.

Two. What is the curve set to and temperatures outside at the moment?

Right now the temperature outside is around 0 °C. The heating is set at 0.4 and the desired room temperature stands at 23 °C, so the flow temperature reaches around 45 °C. The VRC 700 controller is not connected to any room thermostat. My understanding after reading the manual is that the "room temperature" value is used together with the hearing curve value to influence the desired flow temperature.

What's the buildings insulation levels like? A well insulated building will require a lower heat curve and vice versa for a poorly insulated dwelling.

The building has no modern insulation, just a 5 cm of Heraklith on all the inside walls as it was the standard in Austria 60 years ago. We plan to isolate the building later this year. From what I've seen the roof floor is not isolated at all and we might lose a lot of the heat through there.

It's possible that the section where the split is made (the last photo) has been plumbed incorrectly. There are two gate valves that would act as balancing valves if they were on the other side of the branch and the colour coding of the insulation looks incorrect to me.

The way that the pipes are split is really bugging me. I'm wondering if this could be achieved in nicer way, I don't know exactly how. Here are some things that popped up in my research:

• using a smart valve when splitting the circuits, that does the splitting between heating circuits automatically
• move the upstairs heating to a separate controlled circuit, that has it's own pump and valve. My plumber said this is not needed for such a small house, but I'm not sure..

I've managed to increase the temperature upstairs with 1.5 °C by closing by half the valve for the ground floor circuit.

The actuators on the downstairs zone are all present and so is a control box.

Upstairs I did not install any automation system for the heating and left the valves for all the circuits fully opened.

Thanks a lot for the input guys!

 

[SJB060685]

Yes you appear to have read the manual correctly. From what I’ve read on heat curve 0.4 and an outside temp of 0 degrees the boiler should maintain a flow temp of about 35 with a target room temperature of 20 degrees, plotting lines for a target temperature of 23 degrees is going to maintain a flow temp of about 45 as you say. These settings and temperatures are ideal for UFH, in fact without your mixing valves and a higher temperature, say 65 you are likely to cause damage to any screed or floor types.
Like I said insulation levels are a big factor for UFH, this could very well be adding to your problem.
You say you’ve managed to increase upstairs by 1.5 degrees by partly closing ground floor valve? This is telling me the system has potentially not been balanced or commissioned correctly. You may find that if commissioned correctly then you will achieve desired flow and temperatures without the need for an upstairs circuit pump. Over here we generally use one pump and blending valve per manifold and zones, each controlled by its own dedicated zone valve.