Underfloor heating is not getting warm - 20,000 kWh consumption

Hello everyone,

I am writing on behalf of my parents-in-law, who are having problems with their heating system, specifically the underfloor heating. It is a single-family house built in 2005 with a Buderus boiler/water storage tank and underfloor heating. The house has 130 sqm and only one floor. I was shocked to find out that the two of them consumed 20,000 kWh of gas last year... However, I do not find the house properly warm. 2-3 rooms (home office, bedroom) for example are not heated at all... The consumption is really high already...

In fact, a heating technician comes once a year to carry out maintenance. They have a proper maintenance contract. But when asked questions like "why is it not getting properly warm," he doesn’t want to commit and answers: "We did not install the heating system..." They are lucky if the maintenance costs only 300 €, often it is more expensive... He has now suggested as an alternative to replace the heating system at a cost between 5,000 € - 8,000 €...

A few things currently puzzle me, for which I might get help here:

1) They have to refill water in the heating circuits every 5-6 weeks... I understand refilling something once a year with our heating system... but every 5-6 weeks?? They searched for damp spots with moisture meters... everything is dry.

2) In the photo of the heating circuit distributor, you can clearly see that all flow meters are almost at 0... since I don’t have something like that with my underfloor heating, I don’t know what this means... but 0 does not sound like much at first.

3) The pipes all stay cold to at most lukewarm. With my system, you can feel that the pipes get warm during heating operation. I can also read the position of the actuators on my system. With theirs, this somehow doesn’t work. The small valves can be easily pressed down with a knife or something similar.

4) They also “wonder” why our tiles are always nicely warm... noticeably warm so that you can walk barefoot (and the three of us consume 12,000 kWh). Their tiles remain cold... you don’t freeze but they don’t get warm either. Is it somehow possible to check if simply too much screed was used or if the heating loops are simply too deep?

So many questions despite the maintenance contract... I already thank you for your tips and advice...

Best regards, Bros

You can basically only have another plumbing company come and inspect it?

Test: Open the heating circuit distributor box. Turn all room thermostats to 30 degrees. Now the thermostatic valves in the distributor should open within about 15 minutes. If they do not, the boiler is basically heating against a wall. Why the maintenance service doesn’t check this, no idea. Karsten

Now the thermostatic valves in the distributor should open in about 15 minutes.

Hello Karsten, thanks for your feedback... How can I tell if the thermostatic valves are open? So should I be able to recognize this on the actuators or in the picture above on the things that sit on each circuit?

First of all: Just as Karsten says.

But I don’t see the water loss explained like that yet? Since you have no damp spots, it almost sounds as if with 20,000 kWh per year water is mainly evaporating somewhere...

Does the maintenance contract specify the special [Sanitär]? I would definitely get a second opinion!

There are probably several issues. First, really open all the valves. Then it will probably already get too warm everywhere. But it takes some time. By the way, tiles don’t have to be noticeably warm with underfloor heating. The goal is as low a flow temperature as possible.

Water loss can come from a broken membrane expansion vessel. Water expands when heated. If the vessel is broken, it will just vent. That way water is missing in the system.

By the way, it is also bad not to heat individual rooms at all. Since all rooms are in a thermal envelope, the other rooms then heat the "unheated" ones. This comes at the expense of efficiency, as a higher flow temperature is needed in the other rooms.