Ufh and rads combi help

[Russ P]

Ok I know everyone is going to tell me buffer tank but im looking at the system without a buffer tank.

 

I am planning on running a underfloor heating system in 1 room and rads in rest of house. Running of the boiler with a  separate stat on the ufh. It's a combi boiler.

 

do I still need the ufh pump on the manifold and also do I need to put any 2port valves in anywhere to run the 2 Seperate stats

[PeterW]

So you will need to watch this one carefully or the UFH will overshoot big style. It’s about the only situation you want an undersized boiler too ..!

 

You can use a 2 port to isolate the UFH but you need to know if the boiler has a separate pump or if it’s in the boiler itself ..?

[Russ P]

It's a Worcester boiler so I'm guessing pump is in boiler.

do I want a 2 port valve on ufh and 1 on rads? So I can control separate?

 

[PeterW]

How well insulated is the room with UFH ...?? And what size is it ..?

 

For single rooms you’re sometimes better using this sort of thing off the rad circuit  

 

https://www.underfloorheatingsupply.co.uk/Single-room-thermostatic-valve?gclid=EAIaIQobChMI7s6RlYHs1gIVERIbCh16YgGXEAQYASABEgJVEPD_BwE

[Russ P]

It's 2 55metre runs. My boiler is sat right above my ufh manifold in the same room. My main question is.... do I need the circulating pump on the manifold with it being connected to a combi boiler? And to run a thermostat on rad system and thermostat on ufh do I need 2 2port valves?

[PeterW]

How big is the room though..? Is it a new build ..? At 100mm spacing that’s only a 3x4m room so won’t need lots of heating - running it off one single unit on the rad circuit may be quicker. 

 

You may not need a pump if you do it right however if there is a pump in the boiler you have to work out how to control it by both stats. A new controller with two time programmes may be a start. 

[Nickfromwales]

28 minutes ago, Russ P said:

It's 2 55metre runs. My boiler is sat right above my ufh manifold in the same room. My main question is.... do I need the circulating pump on the manifold with it being connected to a combi boiler? And to run a thermostat on rad system and thermostat on ufh do I need 2 2port valves?

Off the combi you need the 22mm flow going into 3 tees, one to a zone valve for heating, one for the zone valve for Ufh, and the third for an automatic bypass valve ( ABP ) so the boiler can recirculate back on itself. 

Room stat to the rad ZV brown wire, second room stat to the Ufh ZV brown wire. Boiler LS ( 'live send' on the WB iirc ) to both orange ZV wires, and both grey ZV wires to LR ( 'live return' ). The brown wire of the Ufh ZV also supplies the manifold pump. 

The stat tells the ZV to open instead of telling the boiler to fire.

The ZV tells the boiler to fire so the boiler pump won't start spinning until the ZV is fully open and there is an open waterway.

As the boiler will do pump overrun, after the stats stop calling for heat / get switched off, you will need the ABP to allow the boiler pump to continue to spin ( against both shut ZV's ) back on itself to the boiler during those 2 mins or so of overrun. 

Oh, and get a buffer , your boiler will HATE this setup, but it'll work. 

You need the pump on the manifold as the pump needs to pull hot water THROUGH the TMV according to the demand of the Ufh. You can't push water through the TMV with the boiler pump, it just won't work. You could effectively do away with the boiler pump,  but you can't as its needed for DHW and the rads so forget that plan .

Look at the Ufh circuit as a figure of 8. The first loop circulates hot water from the boiler, last the TMV, and back to the boiler return. As the TMV opens to heat the Ufh loops to a much lower temp, the manifold pump pulls hot water into the other side of the circuit ( the Ufh pipe loops ) and allows cooled return water to be transferred back to the boiler to be reheated. The TMV retains some of the spent / cooler water form the Ufh loops to blend with the boiler hot to maintain the lower TMV set temp. 

What model / age is the boiler? I hope it's a modern one that can modulate . 

 

Oh, and get a buffer  , your boiler will HATE this setup, but it'll work. 

[Russ P]

6 hours ago, Nickfromwales said:

Off the combi you need the 22mm flow going into 3 tees, one to a zone valve for heating, one for the zone valve for Ufh, and the third for an automatic bypass valve ( ABP ) so the boiler can recirculate back on itself. 

Room stat to the rad ZV brown wire, second room stat to the Ufh ZV brown wire. Boiler LS ( 'live send' on the WB iirc ) to both orange ZV wires, and both grey ZV wires to LR ( 'live return' ). The brown wire of the Ufh ZV also supplies the manifold pump. 

The stat tells the ZV to open instead of telling the boiler to fire.

The ZV tells the boiler to fire so the boiler pump won't start spinning until the ZV is fully open and there is an open waterway.

As the boiler will do pump overrun, after the stats stop calling for heat / get switched off, you will need the ABP to allow the boiler pump to continue to spin ( against both shut ZV's ) back on itself to the boiler during those 2 mins or so of overrun. 

Oh, and get a buffer , your boiler will HATE this setup, but it'll work. 

You need the pump on the manifold as the pump needs to pull hot water THROUGH the TMV according to the demand of the Ufh. You can't push water through the TMV with the boiler pump, it just won't work. You could effectively do away with the boiler pump,  but you can't as its needed for DHW and the rads so forget that plan .

Look at the Ufh circuit as a figure of 8. The first loop circulates hot water from the boiler, last the TMV, and back to the boiler return. As the TMV opens to heat the Ufh loops to a much lower temp, the manifold pump pulls hot water into the other side of the circuit ( the Ufh pipe loops ) and allows cooled return water to be transferred back to the boiler to be reheated. The TMV retains some of the spent / cooler water form the Ufh loops to blend with the boiler hot to maintain the lower TMV set temp. 

What model / age is the boiler? I hope it's a modern one that can modulate . 

 

Oh, and get a buffer  , your boiler will HATE this setup, but it'll work. 

Thanks for that. I know I know I need a buffer tank but I've looked high and low and without ripping my entire bathroom apart again (not and option lol) I have nowhere for it.

i came across a picture finally last night off wunda 

[Scotster]

Hi Russ. That's a nice quick description which is just what I was looking for to help me out. I have a Vallaint ecotech plus currently running HW and CH on an S plan. Ive just had a single zone UFH installed in a large kitchen but not yet wired. It has a typical ZV, TRV and APB set up. To give the engineer who is doing the wiring a running start I did some research on how to integrate my Tado system and it seems fairly clear and your description gave me the final clue. I was wondering if the manifold pump should be fed by the UFH Tado wired thermostat or the ZV orange wire. You say brown wire meaning the manifold pump will run as soon as the Tado UFH thermostat demands heat. See my diagram, my wires are the wonky looking ones! The only question I have is that this means in a situation where the UFH TRV does not need any hot water and is closed and the CH ZV is off BUT the UFH Tado thermostat IS demanding heat the Boiler pump may well run which will force flow either through in the internal boiler APB of the external fitted one. It seems that you think this is not ideal but acceptable? I thought the APB was kind of for 'emergencies only' but here it may be used much more frequently. Can you advise on what bypass pressure should be set at please or how I can figure it out. Many thanks! I have yet to understand what a buffer is but thats my next research as I dont have one...