Underfloor heating and radiators

OK thanks. I have been looking at thermal stores etc and am pretty confused! I already have an unvented DHW cylinder (Gledhill torrent) I presume I don't have to get rid of this? the buffer tank is just an empty cylinder with tappings, the hot water from the boiler goes into this the I have a tapping to go to the DHW cylinder, Another tapping to go to the UFH and a third tapping to go to the rad circuit, the primary fluid is therefore the same for all. Or do I get a tank with a coil, so the boiler goes through the coil then indirectly heats the water in the tank and then the same tappings as above. If I use the method with a coil, then the pump in the boiler covers that bit, the pump in the UFH covers that bit and so I will need a pump for the DHW and Rad circuit, is that right?
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Yes. The boiler circulates to and from the buffer tank using its own pump and a suitably positioned thermostat, maybe the boiler stat will be OK. Each of the other circuits should have its own pump and thermoststs.

You could just use a low loss header as a buffer between all the individual circuits but the buffer tank sounds preferable with the pellet boiler which I assume is less controllable than either a gas or oil boiler.
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Thanks. Would you say running the boiler indirectly through a coil is a better idea than direct. I like the coil idea because the boiler circuit is then really simple and should not be as susceptible to leaks so I can keep the circuit well protected with inhibitors. The pellet boiler is very susceptible to pressure drops although I haven't had to adjust or top up in more than 4 months, so maybe I'm just paranoid.
I'm now going to ask someone to stick their neck out and recommend a product / manufacturer, contentious I know but better than me taking a stab in the dark.
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Just had an idea and want to float it. My original post was because my rads didn't heat up when the UFH circuit was on. What if I use a 3 port valve at the flow to the rad circuit, then use the return from the rad circuit to the flow on UFH circuit. The valve will allow the UFH circuit to still run if the rads are off, if they're on then the temp drop across the rads at ~12 deg is still good for the lower temp UFH circuit. does this make sense or any other ideas how I can get the system to favour the rad circuit. I am trying to avoid adding new pipe runs as this could be a headache.

I can still add a buffer to improve pellet boiler performance.
Don't go down the route of mixing returns where flows should be.
Just won't work.

First thing you should do is check the flowrates on the manifold to each loop.
Should be no more than 3/L min.

Check the pump speeds. You could try lowering ufh and raising the pellet boiler pump speed.

The ESBE valve will move into bypass mode to protect the boiler return reducing flow to the rad circuit.
If the pellet boiler struggles with the UFH then this by-pass operation may be sustained to the detriment of the radiator circuit!
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OK, I'm looking at using a buffer anyway. One supplier is recommending 20l per kwh as it's a pellet boiler that modulates, and any size buffer (as big as I can fit) should help get the circuits working properly.

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