New two channel programmer, heating not coming on

[Johnny2R]

I posted an earlier thread about getting a replacement for an ancient Danfoss 3060 mechanical timer for the heating and hot water. I settled on a Danfoss FP720 in the end, and got an electrician to do the wiring as a new backplate had to be fitted. This was done Saturday.

It's working fine for the hot water (which is a gravity fed system) but as it's a bit chillier today, I went to try out the heating, and what seems to be happening is that the pump is kicking in but the boiler is not firing up.

Now, I wonder whether this is because the programmer has not been set up correctly for gravity fed hot water? In the blurb on the website I bought the FP720 from, it says: "Additionally, the programmer can be set for either ‘pumped’ or ‘gravity’ hot water." I cannot for the life of me find out how or where this setting can be done, though. There seems to be nothing in any of the manuals I've looked at and Danfoss customer service have not so far responded to me.

I am assuming the wiring was done correctly, but is there a possibility this behaviour could be explained by a wiring error?

 

[Murdochcat]

If you paid a spark to make the change THEN GET THEM BACK.

 

[Johnny2R]

He'll come back, certainly. I'm fairly convinced at this point, though, that the issue is that it's currently working as if it's a fully-pumped system whereas it needs to be set to gravity-fed. Frustratingly, not only can I not find out how to do this, I'm not even sure it can be done. I've seen this sentence "Additionally, the programmer can be set for either ‘pumped’ or ‘gravity’ hot water" on a few other websites now as well, but I'm not sure it's actually true. I'm kind of assuming that if it isn't, then the company I bought the item from should take it back.

 

[ericmark]

There are three C Plans, basic, one with tank thermostat for summer use, and one with tank thermostat and motorised valve, so DHW will not over heat in the winter. The programmer activates just the boiler for DHW, and both boiler and pump for central heating and most had a slide and switch to select how they work.

However there is nothing to stop this being manually selected. The slide on the old programmers simply stopped the user selecting CH without also selecting DHW.

I use Nest Gen 3 for DHW but there is no way to select CH only, you can only select DHW only, in summer I find cheaper to use the immersion heater for DHW, typical need 25 kWh oil boiler to get DHW for week, and 5 kWh using the immersion heater, so boiler only used if I want a bath, as immersion heater only heats the top of the tank.

I found having a single wall thermostat for the CH did not work in my house, so I have three, the other two are Drayton Wiser. But you will note from diagram one if set for DHW the boiler is active even if the tank is hot, and it is the hot return water which stops it running, so one has to take a guess on how long it needs to run for, I found from experiment needs 4 x ½ hour runs per week in summer, winter don't need anything as runs for long enough with the central heating.

So however I set it up using boiler for DHW some times boiler would run for too long, resulting in unlagged pipework being hot, we should maintain the tank at least at 60ºC to stop legionnaires, but near impossible to set this up using a boiler and no tank thermostat.

If using an immersion for summer, then only reason to run boiler for DHW is to have a bath.

 

[Johnny2R]

@ericmark , thanks for your detailed response. But I'm not sure how it helps me? I need a means of doing what you say: "The programmer activates just the boiler for DHW, and both boiler and pump for central heating and most had a slide and switch to select how they work." I don't see any means of doing this via the control panel and there are no dip switches on the back to set.

 

[ericmark]

I have a box with a relay, should really have two, if not built into the programmer then either one where it is built in, or a relay. I had to consider here what to do, Hive has the software fix, but Wiser has better TRV heads, Nest Gen 3 has the common you can use, but will not link to the TRV heads, central heating is always a compromise, and it's up to you what you accept.

I call it near enough engineering.

I note * have you tried press and hold for 3 seconds and what does it give you?

 

[Johnny2R]

"I note * have you tried press and hold for 3 seconds and what does it give you?"

It gives access to a bunch of parameter settings, 7 in all, covering things such as 24hr/12hr clock, auto daylight savings time, 1/2/3 periods a day, etc. Unfortunately fully-pumped/gravity-fed is not one of them. I'm becoming increasingly convinced that the FP720 is actually incompatible with gravity-fed hot water systems and I should have gone for something like the Drayton LP722 (which has a dipswitch). It just puzzles me that so many sites repeat the same thing in the blurb: "Additionally, the programmer can be set for either ‘pumped’ or ‘gravity’ hot water"

 

[CountryFan]

I would contact Danfoss technical and if not supported, it could be returned as not as described and not fit for purpose

 

[RepairingDave]

The silly question first: Have you got a thermostat and was it turned up far enough to make the boiler turn on?

Also, does the heating come on when both the hot water and heating is turned on?

 

[cider]

Usually a little switch on the back or a link to move. The heating relay needs to activate the hot water relay for gravity hot water. It seems to not be a feature on this particular model. You either need to exchange it or you could install an external relay to turn the boiler on with the heating. Realistically it will be more expensive to do so and your average electrician won’t know how to. Given your electrician didn’t spot the issue you are encountering I wouldn’t even ask them to swap the programmer. Perhaps Danfoss do another model with gravity hot water option which will fit straight on to your backplate so you can do this yourself. If you don’t want to spend any more money you could just set the heating on time the same as the hot water to bring the boiler on.

 

[DP]

Might be parameter P3.
Call Danfoss and seek guidance from them

 

[DP]

The silly question first: Have you got a thermostat and was it turned up far enough to make the boiler turn on?

Also, does the heating come on when both the hot water and heating is turned on?

Pump is running to circulated heated water but boiler is not being activated to heat water. Pump is responding to heat call
So, thermostat is calling for heat.

 

[Johnny2R]

I sent Danfoss customer services an email a few days ago, to which they have not yet responded. It would be good to know whether what I'm trying to do is even possible, of course, otherwise I'll have to swap out the programmer.

Yes, I did try turning up the thermostat to the highest temperature, without any effect. But surely the fact that the pump has kicked in is an indication that the system is responding to demand, but it's just not working right because the boiler isn't firing up? Presumably if it was the case that the room temperature was already high enough, the pump wouldn't run? (I think this is what @DP is saying, too).

Parameter P3 is 'Channel Setup' and has two options:

01: Heating + Domestic hot water
02: Two heating zones

It is currently set to 01. I don't think this is relevant, unfortunately, unless I've misunderstood something.

I would contact Danfoss technical and if not supported, it could be returned as not as described and not fit for purpose

The electrician is blameless here, I have to say, as he himself spotted the problem the other day, but between us we couldn't work out how to resolve it, assuming that the resolution is somehow switching the programmer to gravity-fed mode (it was me that ordered the FP720). As far as I can determine it was wired just fine, but the device itself does not do what it was advertised as being able to do. I'm hoping that I will be able to simply clip in something like a Drayton LP722 as a replacement, without any rewiring necessary, as both appear to use the industry standard backplate.

If you don’t want to spend any more money you could just set the heating on time the same as the hot water to bring the boiler on.

So should the central heating actually work as long as the hot water is on?

 

[CountryFan]

The electrician is blameless here, I have to say, as he himself spotted the problem the other day, but between us we couldn't work out how to resolve it, assuming that the resolution is somehow switching the programmer to gravity-fed mode (it was me that ordered the FP720). As far as I can determine it was wired just fine, but the device itself does not do what it was advertised as being able to do. I'm hoping that I will be able to simply clip in something like a Drayton LP722 as a replacement, without any rewiring necessary, as both appear to use the industry standard backplate.

I didn't say he was to blame.

 

[Stuart981]

"I note * have you tried press and hold for 3 seconds and what does it give you?"

It gives access to a bunch of parameter settings, 7 in all, covering things such as 24hr/12hr clock, auto daylight savings time, 1/2/3 periods a day, etc. Unfortunately fully-pumped/gravity-fed is not one of them. I'm becoming increasingly convinced that the FP720 is actually incompatible with gravity-fed hot water systems and I should have gone for something like the Drayton LP722 (which has a dipswitch). It just puzzles me that so many sites repeat the same thing in the blurb: "Additionally, the programmer can be set for either ‘pumped’ or ‘gravity’ hot water"

If your FP720 has an industry standard backplate and your sparky wired it correctly then you could swap it for a Drayton LP722. I have a LP722 controlling pumped heating and gravity hot water. It replaced a mechanical controller that had an industry standard back plate meaning it was a matter of just swapping over the controllers and selecting the switch on the back to G.