My system is similar to yours.

Some preassembled manifolds are designed to bolt into an existing rad system without TS and have a bypass on them where the boiler flow and return connect. This is intended to allow the boiler pump to continue to circulate water to the rads when the UFH mixer is fully recirculating.

If this type is used with a thermal store and no rads they need a pump to circulate water from the store to the manifold and back.

Personally I feel this is a mistake, not least because it stirs the store. Other manifolds don't have a bypass and can use the loop pump to draw water from the store through the mixer.

My builder purchased this type of manifold and I was going to remove the bypass instead of using a pump but he was worried about the warranty pressed me to fit a pump. I fully intended to remove the pump and bypass some day but never got around to it.

It is set up with bypass valves to control the return temperature to the" boiler" which should be hotter than the return temperature of the u/f heating loops but in my case it is not as the return to the store is the same temperature as the loops.

Did you mean a bypass or is there also a mixer to control the return temperature? I have such s mixer on the primary side of my store to control the boiler return temperature. As I recall Grant say this must be >40C for their oil boilers.

My usual caveat on responses here is that this is my understanding, based upon your interpretation, so obviously without seeing the installation, there's an element of uncertainty, but here's my thoughts...

1. you're right to keep the bypass from flow to return closed, as you're not linked to the boiler, so def do not want bypass back to the TS. This is one of the reasons I normally include TS's in my designs, so there's no link between needing UFH, and the heat source having to run (stops short cycling, amongst other things etc)

2. "sounds" like you have dual temp control for the feed water, ie. safety over ride in case of the TMV failure.

3. I'm not clear (like you) why there is a needle valve to control the cool return water flow rate into the TMV, as I would expect the TMV to control how much cool return it allows to mix with the hot feed, since that's what delivers the set temp. May be worth asking Robbens to explain exactly what that valve is for, and for what circumstances.

4. Makes sense that the flow rate of the long (non-achieving) loops will drop a bit, as you open up all the other valves, since that's a function of the pump curve, (increased flow, reduced head)

5. speaking of pump curves, I can't quite read the pump label, but it looks like an Alpha 2L, not sure if it's a 50 or 60? This has various settings for pump performance. If you set it to "III" for the moment, that will give constant speed, and so the highest possible flow rate for any given pressure.

6. The pump's pressure will be determined by the index leg, or the loop with the highest pressure drop, likely to be the longest loop. That then fixes the max poss flow rate from the pump. It's not really the total length of pipe, since the loops are in parallel. Make sure the adjustable valve on this leg of the manifold is fully open. From memory, you can alter that at the brass body under the little black plastic flow setter. In other words, you can do a gross adjustment at the brass body, then fine tune that with the black plastic twiddler. You need to make sure for that index loop, and any other loops very close in length, that you have the minimum possible resistance at that flow setting point. Sometimes the factory set position is a middle point.

7. If you have ascertained that the longest loops/loops are now at the least pressure drop possible for that length of loop, and the flow rate still is not adequate, then you may well have to add another pump in series to augment the loop pressure. How far away from the stipulated flow rate for these couple of long loops is the actual? Do you know that it will in fact be inadequate to keep that/those rooms warm in winter? Calculations of flow rates and heat loss, and heat requirement are subject to many influences, not least of which people adding in lots of insurance by way of conservative numbers, which can add up to implying you need a lot more flow than you actually do.

8. Gravity doesn't have any effect in a closed loop, since what goes up, must come down. It's only the additional length of pipe, that would then caused a pressure drop. I don't understand your comment about water rising upstairs. Are there UFH loops upstairs? Do they come off this grnd flr manifold?

9. You mention you very quickly run out of heat in the TS in the zone that the UFH draws from. What is the Total volume of the TS, and what volume is between the UFH flow and return connections? It does make sense that when the UFH first calls for heat from the TS, say in the morning when the night set back flips to morning room temp setting, the water in the loops will be cool, so there's a sudden large surge of cool water returning to the TS, to it will take a while for the TS to catch up. The volume questions above will say more about that. Also make sense that when the boiler pump starts running, it initially destratifies the TS, as the flow is likely in to the high point on the TS, and the return near the base, so it pushes hotter (normally DHW) water, down the store towards the boiler return connection, which is also down towards the UFH flow connection.

Hope there's something in all that which helps.

Thanks for inputs doing some more testing /adjusting will report back later.

I think the TS loop pump can be controlled from whatever generates the signal for valve T1 (see photo earlier).

If you have two manifolds (eg two valves) you need to devise a circuit that performs the logical OR function so the TS loop pump turns on if either manifold A OR manifold B calls for heat.

My plumber originally wired the TS loop pump to run continuously! So I built a control box that performed this logical OR function using two relays.

Sorry for not replying sooner. Not sure I understand your question. The mixer is thermostatically controlled so it decides what ratio of new hot to cold return is required to achieve the required/set output to the floor loops. Bit like a shower mixer. You set the output temperature and it controlls the mixing ratio depending on the temperature of both the hot and cold water. Sorry if I'm teaching grandma to suck eggs.

Sorry for the long delay again!

Posted By: GreenPaddyAnyway, the reason that adding a second pump in series, but upstream of the mixing valve is a problem, is as you described above, ie. the signal to run the new/additional pump would come from the actuator valves being in the open position. These valves can be in the open position, but the mixing valve is on full recirc from the cold loop returns, with NO water coming from the Thermal Store, and so NO water being pumped by the new/additional pump, even though it's being told to run...ie. the pump is dead-ended.

It won't be blocked (dead-ended) if there is a bypass from flow (1) to return (6) in your photo above.

The circuit I used to control my TS pump is attached. My system has two manifolds each controlled by a wiring centre. Each wiring center provides a "Boiler Enable" (BE) signal when any of its stats call for heat. In a system WITHOUT a TS these BE signals would be used to turn on the boiler. In a system WITH a TS they can be used to control a pump that circulates water from the TS to manifolds and back. My circuit performs a logical OR function so when either BE1 OR BE2 is active the TS pump is enabled.

Your wiring centres may not generate BE signals (or it may call them something else). However it does have two alternatives:

1) The signals that control the two manifold valves (numbered 1 on your photo). What voltage?
2) The signals that control your two manifold pumps (240V AC)

If BE signals not available my circuit could be wired to either of these so that when either manifold is calling for heat the TS pump will also run.

Notes:

a) The relay coils must be selected to suit (eg if connected to the manifold pumps the relays coils must be 240V AC coils - I don't know what voltage your manifold valves use). The relay contacts must also be specified to switch 240 AC to the TS Pump at quite high current, as the pump may draw quite a bit when it starts. I used DIN relays that plug into a small DIN rail mounted in a plastic box so if the relays ever wear out they can be simply unplugged and new ones plugged in. Been running 12 years so far without a problem.

b) In some systems it might be possible just to connect the two BE signals together and to the TS pump without using relays. However there is the possibility that the BE signal from one manifold might feed power back _into_ the BE signal from the other manifold causing both manifold pumps to run when only one should. The relays keeps the two manifolds isolated.

A good electrician should be able to make sense of this.

Apologies for not replying sooner having hectic time with empty promises and non delivery or damage to goods. So many thanks for the quality replies.
Situation is that got all the loops commissioned at their required flow rates all at the same time apart from the one loop that did not achieve the design flow rate even though I valved off all the other loops. This loop is one of the longest and spaced at 150 mm. Robbens advised that the system is designed to have a pumped supply to the manifolds so this may be an addition for the future. Will see how the system performs over the winter months. The affected loop is in a glazed entrance way that resembles a lean to green house. ( It will be used to overwinter our tomato cuttings) As it is not a living area it may not work out that much of a problem.
As for controlling a pump that will not be an issue as the Robbens controller has a boiler output so that when the loops call for heat then this output triggers the boiler. As this is "spare" because my boiler is controlled by the TS thermostat, then the pump can be controlled by the boiler output on the Robbens controller. I played about a little with the manifold mixer valve and allowed a little flow back to the TS seemed to work.
Not been able to run the system yet as floor has only just finished being tiled. Been too warm for heating anyway and getting the benefit of the high levels of insulation and the solar gain designed into the build.