Underfloor Heating Stealing Water from HW Cylinder

Bornagainbiker

I an currently upgrading my UFH system and have noticed that the Underfloor Heating Manifold and Hot Water Cylinder are robbing each other of water!!! This has probably been going on for years, but I'm only discovering it now.

What is most notable is that the underfloor heating pump is sucking water from both the oil boiler and the hot water cylinder (acting almost like a mixing valve). The underfloor setup is teed directly off the main feed from boiler to hot water cylinder.

This is resulting in the hot water in the cylinder being drawn off into the floor,

I am proposing to install a two port valve on the return pipe from the cylinder, as the system is open vented and I don't want to impede the flow pipe in case the water needs to expand into F&E Tank.

Can anybody tell me if this is an acceptable (safe) solution? The pump for the hot water cylinder is also on the return pipe!!

antoinolachtnai

You need to draw out a little diagram for us. How come the hot water cylinder has its own pump?

There must be some sort of heat exchanger or mixing valve in the system somewhere (I suppose) and it is important to understand where and how.

Longboard

Bornagainbiker wrote: »

I an currently upgrading my UFH system and have noticed that the Underfloor Heating Manifold and Hot Water Cylinder are robbing each other of water!!! This has probably been going on for years, but I'm only discovering it now.

What is most notable is that the underfloor heating pump is sucking water from both the oil boiler and the hot water cylinder (acting almost like a mixing valve). The underfloor setup is teed directly off the main feed from boiler to hot water cylinder.

This is resulting in the hot water in the cylinder being drawn off into the floor,

I am proposing to install a two port valve on the return pipe from the cylinder, as the system is open vented and I don't want to impede the flow pipe in case the water needs to expand into F&E Tank.

Can anybody tell me if this is an acceptable (safe) solution? The pump for the hot water cylinder is also on the return pipe!!

from what you described, I'm assuming the sytem looks something like this . . .


Why not consider check valves on the returns before the T?

Bornagainbiker

Longboard / antoinolactnai,

Thanks for your replies.

Longboard, your diagrams are on the button. This seems to be exactly what is happening.

There are two pumps, one on the flow to the UFW (after mixing valve) and one on the return from the cylinder. I've no background in plumbing so I can't explain why the system is plumbed this way or if it correct or not.

There is a shut off valve on the return from the cylinder, and when I close this (for testing purposes only), then the UFH pump seems to work as intended (i.e. supplying hot water from boiler ONLY).

If I put a check valve on the cylinder return, will this have any negative effect on the flow if it needs to pitch into the expansion tank in attic?

Scudo.2

You have a system fault.
Call the experts as both systems should work independently.

K.Flyer

Bornagainbiker wrote: »

Longboard, your diagrams are on the button. This seems to be exactly what is happening.

There are two pumps, one on the flow to the UFW (after mixing valve) and one on the return from the cylinder. I've no background in plumbing so I can't explain why the system is plumbed this way or if it correct or not.

There is a shut off valve on the return from the cylinder, and when I close this (for testing purposes only), then the UFH pump seems to work as intended (i.e. supplying hot water from boiler ONLY).

If I put a check valve on the cylinder return, will this have any negative effect on the flow if it needs to pitch into the expansion tank in attic?

It would appear from your explanation and sketches that you may have a system that suffers from reverse circulation.
If the system is as per the sketches, then a solution may be to fit a zone valve to both flow on the DHW coil and one on the flow manifold for the UFH. These would then need to be wired in series with their respective circulation pumps so that the pumps are not pumping against a dead pipe.
In doing this you would then also have to watch out for pitching on the F and E tank and some adjustments may need to be made there also.

Bornagainbiker

Thanks for all the advice Guys.

The underfloor heating has actuators, which I think act as individual zones, and these call for the pump to switch on as and when necessary. If all zones are off then the pump is off too. If any zone calls, then the pump operates.

Would a check valve as suggested by Longboard do the same job as a zone valve, only keep it on the return pipe, so as not to impede pitching to F+E tank?