Wiring for Wet Underfloor heating single Zone

[DIYUFH]

Hello, appreicate this question might have been asked before, I can see similar has been asked in this forum and elsewhere but I'd like to be clear on how to do this, all ideas and comments very much appreciated.

I would like to add Underfloor Heating to an existing combination boiler, my questions are around the electrical/control side, not the plumbing. The existing combination boiler has a built in timer that controls the central heating system which is currently all radiators in a single zone/circuit. I would like to add wet underfloor heating to this which has a pumped manifold. I am aware that the usual means to add Underfloor Heating is to connect it as a separate, second zone, with it separated using zone valves and the thermostat for the underfloor heating triggers the boiler to provide heat via the Switch Live electrical input on the boiler. However......
A. My boiler does not have an electrical output to connect a zone valve, so when the built in timer on the boiler goes to turn on the radiator central heating, there is no means for it to actuate a zone valve
B. I only want the underfloor heating on at the same time as the radiators, there won't be an occassion when the radiators and underfloor heating are on at different times, so no need to have this in a separate second zone. As such, I want to plumb in the underfloor heating manifold (blending valve) to the main central heating circuit so the whole system remains as one zone. I don't see the benefit in using zone valves as my house is not big enough to warrant multiple heating zones and I can see others are not recommended zoning heating anyway.
C. My boiler does not provide an electrical output to connect an external pump, so I don't see a means to connect the pump on the underfloor heating manifold to the boiler.

I can think of 2 ways to achieve what I want:
1. Provide some sort of feed from the timer on the boiler to turn on the pump at the underfloor heating manifold. I think this will need some sort of relay and an electrical connection from the boiler, though unclear as to how this can be provided.
2. Disconnect the built in timer in the boiler, instead use an external timer that controls both the underfloor heating and the main central heating. This will necessitate providing a Switched Live connection from the timer to the SL input on the boiler. This looks to be the best solution.

Any comments/ideas?

Many thanks.

 

[EFLImpudence]

It would seem there are questions around the plumbing side.

Zone valves activate the boiler and so pump; not the other way round.

 

[DIYUFH]

Thanks EFLImpudence. My understanding is that the switched output of the Timer can be connected to the Switched Live intput on the boiler, it does not need to go through a zone valve. The installation instructions supplied with the boiler show this arrangement. This would appear to be the best arrangement for what I want to achieve - disconnect the boiler's internal timer and have the whole thing controlled from the programmer/timer for the underfloor heating.

 

[EFLImpudence]

I refer the honourable gentleman to 'A' and 'B' in his original post.

 

[Collectors]

You might find zoning a better idea as underfloor heating has different characteristics from radiator heating & will possibly need longer times. In the winter many systems run 24/7 but have ways to cut the boiler back to just a tick over for 2/3rd of that time because of the under floor heating taking a wile to heat up. Depending on your layout a programmer & a couple of motorised valves would sort it as any boiler can be made ok for this.

 

[ericmark]

My central heating is split into around 14 zones, of these 4 are in one sub-zone, and 10 in another sub-zone, the TRV forms a zone, so I have two pumps, with two zone valves, to separate the flat to main house, as often the flat is not used in winter, so good to be able to turn off 4 zones with one valve and pump, but the main house has 9 programmable TRV heads, the shower room and upper bathroom being heated all the time the boiler is running.

So ignoring the flat, the main house has two programmable thermostats in parallel which can activate the boiler, one Nest Gen 3, the other a Drayton Wiser, the intention is to fit Wiser TRV heads in the future, but at the moment none of my TRV heads are linked to the hubs which activate the boiler, pump, and motorised valve for the house, when the time and temperature are such that the boiler runs, then the TRV heads decide which rooms are heated, by how much, and when, without any wireless or wired connection to the boiler.

The same applies to your underfloor heating, when the boiler is running the pump and valve can heat up the floor without any electrical connection to the boiler. All it requires is a water temperature sensor to turn off the pump if the water is not hot.

The exactly same way as a fan assisted radiator works, the water flows though the radiator when ever the boiler is running, and it does not heat the room until the fan starts, and for the fan to start, the pipes have to be hot, and the room needs to be cool, there is no electrical connection between the radiator and the boiler.

The problem arises in trying to control the boiler by the return temperature of the water, I found this with the fan assisted radiator, pre-modulating boiler, it did not matter what the return temperature of the water was, but as we went to condensating boilers with modulation controls, the return temperature became important.

So with all fan assisted radiators the method was plum in series, not parallel, but with all TRV control plum in parallel not series and add a by-pass valve, the problem arises when one tries to mix the systems. This is a plumbing question, the underfloor heating would be plumbed like the fan assisted radiator in series, but the simple radiator with TRV heads wants to be in parallel, or the boiler can't gain the latent heat from the flue.

Electrically wise easy, it is the plumbing which is the problem. You have one which want series and another which wants parallel, the easy method to me is all series and use fan assisted radiators.

The fan assisted radiator does seem the way to go, the ivector had 5 fan speeds, but the building management system to go with it costs an arm and a leg, likely we will all need to move to fan assisted radiators in the end, as these can both be used to heat and cool, and if we accept we have globule warming then in the future we will need to cool our homes, so to have a single system with heat pumps rather than boilers that can both heat and cool makes a lot of sense.

The problem is most homes are plumbed in parallel and this will need changing to series, and also all pipes will need to be lagged, or condensate on pipes will cause a problem, and all radiators will need a condensate pump to remove the condensate. And of course underfloor heating is really a non-starter, sorry.

 

[flameport]

Any comments/ideas?

Where is the room thermostat in all of this mess?

 

[DIYUFH]

I appreciate everyone's reply, thank you all.

My question was whether I can use the timer that is built into my combination boiler to switch on the pump attached to the underfloor heating manifold. I think I have that answer and that is no, no it can't as there is no electrical output from the timer to control external equipment.

Therefore, the only option is to disconnect the timer that is built into the boiler and instead use an external timer/thermostat that is connected to a "wiring centre" where the output of that wiring centre is connected to the external control input on the boiler. So when the external timer/thermostat calls for heat, it will switch on the boiler and the pump on the manifold. In order for that call for heat to happen, both the programmed time and the thermostat temperature have to be true.

As I will have the underfloor heating and the radiators in the same plumbing circuit, i.e. 1 zone, this will turn on both the underfloor heating and the radiators at the same time which is what I want. I did do quite a lot of research into multiple heating zones and the advice received is not to have multiple heating zones in a simple domestic dwelling that I have where there are no heated outbuildings etc.

Thanks.

 

[ericmark]

I would have thought a pipe thermostat on the feed to the underfloor heating manifold would do the job, if the boiler is running the pipe will be hot, if boiler not running pipe will be cold, in the same way as the fan is turned on/off with a fan assisted radiator.