Balancing of a mixing circuit

Vertical

I have a mixing circuit for underfloor heating which does not seem to get enough heat into it. I've attached a diagram of the circuit.


The boiler is a modulating type (outputing at 80DegC) but does not seem to be the problem; its rated to 24KW and (calculating from the gas meter over an hour) the mixing circuit is only pulling about 10KW from the boiler.
The max temperature on the flow manifold is <40 DegC no matter how the mixing valve is set, this is too low which slows getting heat into the slab.

I'm not a plumber or mechanical engineer, but I suspect that the problem is that the circuit is not balanced and the pump is drawing around too much recirculated water at the expense of flow from the boiler.


1. Should there be a valve in-line with the none return valve on the recirculating pipe?

2. If so is it sufficient to use a gate valve to effect this?


Any suggestions appreciated

kay 9

There should be no need for a balancing valve on that circuit. Has your 3-way valve the ability to manage the flow directions such as limit it to each? Hmm, was it working ok before? Only time I have seen underfloor giving trouble is when it has a leak and that is a pain in the head to find in a maze of pipes:rolleyes:. Not being smart but you do realise that underfloor heating is much more efficient and produces better output if left on low all the time rather than turning it on from time to time as it takes time to heat the floor. Once heated, it doesn;t require much to maintain.

Vertical

Yes the valve will only work with 1 port in and 2 ports out.
Heating system was only installed in the spring so its only getting its first real test now.
Understand about leaving it on all the time, it eventually heats the slab sufficiently so you are right.
However I'm trying to see if I can get the best response from the system which would allow tighter control and therefore more stable temperature around the thermostat set-point.

kay 9

I get where your coming from alright but that's one of the downsides with underfloor is it's not like the conventional rads where ya flip a switch and feel heat in 10-20 mins. Underfloor heating takes longer to heat and longer to cool. Alot of people have found this with underfloor but it is a great system. Will be putting it in bedrooms and bathrooms in my house if I ever get to build in this damn country.

Plombier

Kay 9 is absolutly correct UFH needs to on for much longer periods. You are approaching this in totally the wrong way. Firstly leave your heating on 24/7 turn the temperature to the UFH to its 'lowest' setting leave it for a couple of days if it heats your house at this temperature leave it there, if not increase the temperature by very small amounts each day until the house is comfortable, next turn off the heating for 3 hours during the night(and day if possible) if there is no loss of comfort in the house increase the off time by small amounts, while still maintaining comfort. The weather we are having at the moment is ideal for doing this. Also you should note if this is a recent build the system has to work harder for the first season in drying out concrete etc. If you are more specific about the type of controls you have, the complete system might be more controllably.