Possible Danfoss FP715Si issue

8 Dec 2009
Reaction score
United Kingdom

We have one year old Ideal Logic+ system boiler (not combi) which is controlled by a Danfoss FP715Si in combination with a wireless Siemens room thermostat.

The Siemens is just set to 18/19 degrees and the Danfoss should keep the heating on while it is programmed to do so (e.g. 6pm -10pm).

The heating seems to be coming on when it is set to do so but it is usually only for short periods (30-60 mins) and once it goes off, it does not come back on during the programmed window, no matter how much we up the room thermostat. The room thermostat does appear to be talking to it's receiver buddy correctly.

The 1HR and ALL DAY Danfoss features don't wake it up and it looks like the only way to get the heating back on is by switching off/on the programmer at the wall (reset doesn't work either). After a switch off/on it tends to work ok until the next time.

The boiler just sits there with '0' message which means it's waiting for a heating/water call. Is this a common issue with the Danfoss fp715Si? I've seen a few complaints but there are no obvious errors and the Danfoss isn't doing anything strange when I use it.
Sponsored Links
More likely to be a problem with your Siemens stat.

1. Which model do you have?
2. How far apart are the controller and receiver?
3. How many walls directly between them?
4. Which make batteries in the controller
1. Which model do you have?

RDH10RF (basic features with just the dial)

2. How far apart are the controller and receiver?

Thermostat is in dining room directly beneath the bedroom which contains the airing cupboard and receiver.

3. How many walls directly between them?

Just the floorboards

4. Which make batteries in the controller

Energizer industrial

The boiler is Ideal logic + plus 30kw system

The last house we had the Siemens RDJ10 which went wrong after a year and stopped communicating with the receiver. I replaced it and no problems for next 4 1/2 years. This receiver appears to be communicating just fine. No red lights and flashes/clicks as soon as we up the temp.

I spoke to a few people today who told me that the Danfoss is usually pretty reliable and eventually Ideal said they would come and take a look later this week. However this afternoon I told the missus to switch it off/on (it was not turning on) and since then it has been responding and working as expected. I tried upping the temp a few times and the boiler came on/off instantly. So now I'm stumped. I'm expecting it to play up again so I'll give it another day or so before calling off the Ideal engineer if there is no error to show.

If it was the boiler, what would cause this kind of behaviour? It seems to heat the water ok but I have set the heating/water times so that they don't clash any more as it wasn't really heating the water very well when they were both on.
Thanks for the answers. I know Energiser batteries, but no the 'industrial' versions. Most installers recommend Duracell. However the battery does not seem to be the problem, neither does communication,

My guess is that, while the receiver is responding to the signal from the control unit, the relay inside the receiver, which connects Lx to L1 or L2, is not always operating.
Sponsored Links
OK that does seem like possiblility as well. It's been absolutely fine the past two days now! Typical. If it does flare up again the most economical option may be to get another Siemen receiver, which are not too expensive and if that is not the cause I'll have to move onto the Danfoss - both of which may still be under warranty but I'll need to chase up the previous owner and see when those units were installed.

BTW I had the Energizer Industrial batteries in two or three thermostats before and they always worked very well and lasted a long time.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local