Combi boiler and UFH

[llywelyn111]

Hi,

I had finished a first fix on a timber frame 6 bed house last week, all the customer wanted was standard radiators and hot water off a oil combi boiler. Rang me this morning to say his wife wanted UFH in the kitchen, sunroom and utility. So I went there this morning to run 3 core cable to each zone for him.

I have never done this type of system before on a oil combi boiler before only condensing. Is it actually possible with a combi boiler with no hot water tank etc

any advice please

 

[yellowvanman]

Usually with wet under floor heating there would be a manifold with a number of valves for the different zones, each zone controller would control the necessary valve(s) - best work with a plumber on this.

Trouble is that when the UFH calls for the boiler to kick in then it could backfeed the other calls (hot water & radiators) so you may need to use contactors to seperate the boiler calls - gets a bit complicated but can be done with a little thought!

 

[llywelyn111]

Usually with wet under floor heating there would be a manifold with a number of valves for the different zones, each zone controller would control the necessary valve(s) - best work with a plumber on this.

Trouble is that when the UFH calls for the boiler to kick in then it could backfeed the other calls (hot water & radiators) so you may need to use contactors to seperate the boiler calls - gets a bit complicated but can be done with a little thought!

OK thanks, I'm just use to wiring UFH to it's own wiring centre and radiators and hot water to it's own wiring centre (S plan or S plan + I'm used to doing). Just never done on to a combi. Doubt there is a wiring diagram for one of these is there.

 

[yellowvanman]

UFH usually come with their own control boxes and if applicable slave unit (dependng on number of zones) - there's connections for pump, valve and boiler - its the UFH boiler call that needs to energise a contactor to call the boiler, similarly use a contactor for the hot water and CH calls to stop any back feeding.

 

[ratboymark]

ive done this before on a farm house job it had UFH downstairs and rads upstairs but the was a plumbing issue with the system i think the problem was the combi pumps a load of cold water into UFH then hot so was unpractical so i went the other week to price for the electric side for his new water tank he is having to get but yes wiring is possible but as yellowvanman says it dose take some thought to do it right i supplied a wiring digram with the system incase another spark had to work on the system unfortunatly i dont have a copy the client got the copy (hand drawn)

good luck tho

mark.

 

[llywelyn111]

thanks, for your help. I'm hoping the plumber suggests any boiler but a combi boiler. Might force feed him some beer.

 

[Dale200bhp]

I have done this several times, it depends on the underfloor kit you have, if its robbens or speed fit there is some volt free contacts that close when calling for the boiler, so you just need a 2 core from these to the combi boiler, and the link you take out the boiler connect these which also will be parrelled up to the upstairs rads via a 2 port valve.

 

[llywelyn111]

I have done this several times, it depends on the underfloor kit you have, if its robbens or speed fit there is some volt free contacts that close when calling for the boiler, so you just need a 2 core from these to the combi boiler, and the link you take out the boiler connect these which also will be parrelled up to the upstairs rads via a 2 port valve.

Ok thanks for that. I think it's the Speed Fit UFH system. So hopefully simple enough then

 

[sambotc]

can you not use a 2 channel clock for heating/UFH and wire like an S plan through a wiring centre, then a seperate clock for the hot water? Most oil combi's require a timer for hot water as they have a heat store jacket which is heated up prior to demand (worcester bosch, grant etc)

 

[boldspark]

The answer is quite simple. You need to zone off the rads on a separate valve (or 2 if over 150m2) and wire it up as per normal s-plan.
You MUST get bypass installed, or there is bound to be trouble.

 

[adamh]

A 3 core and earth to each room with the UFH will be fine, and then on the second fix or after speaking to a plumber you will know if its going to be conventional/combi system. The norm as others have said would be for a manifold for the UFH with seperate actuators for each zone and a standalone control panel. But untill you get a spec for the system what you have done so far will do for a 1st fix

 

[yellowvanman]

A 3 core and earth to each room with the UFH will be fine, and then on the second fix or after speaking to a plumber you will know if its going to be conventional/combi system. The norm as others have said would be for a manifold for the UFH with seperate actuators for each zone and a standalone control panel. But untill you get a spec for the system what you have done so far will do for a 1st fix

In saying that the one I've just 1st fixed a system that asked for a 4 core to each room, I put in a 5 core as I wanted an earth at each point as well!

 

[adamh]

your right some will require a four core depending on the stats that you use , it usually depends on if the boiler or the panel is happy with a 230v s/l for a call to heat. If you need volt free then it can be a problem but nothing a relay wouldn't sort out

 

[Gravid]

I've recently been 1st fixing a place where there's ground floor UFH and upstairs radiators off a combi. They where going to use Uponer but in the last few days have changed their minds and are using polyplumb, apparently it's a lot cheaper.
The UFH is 3 zone and the manifold and slave box are going under the stairs, the combi is in the utility on the other side of the house.
I've no wiring diagram, as it stands i've run a 5 core to each UFH stat back to the manifold and a 5 core to the utility, this is what the Uponer rep told the client. Both Uponer and now Polyplumb have told him I just need a supply to the Manifold etc and one switch wire back to the combi is this correct?
No ones mentioned back feed and putting contactors in yet !
Cheers for any advice.

 

[adamh]

assuming your valves are at the combi then yes , your s/l will open the valve to the UFH manifold and at the same time will close the contacts for the call to heat, which will be wired in parallel with the ones on the other valve connected to the s/l from the room stat for the upstairs rads.