SITUATION. Systems all checked:

Pipes flushed, a sparky has checked electrics, new combi boiler (£7.5k ouch) and providing water to required temperature, thermostat calls for heat, a new actuator (replaced 1 week ago), mixing valve checked, pump checked (set at III or II), flow meters showing 1.5, temperature showing 32 degrees.

PROBLEM. Water supply pipes up to manifolds hot but tepid once in manifold. Floor tiles not warming (chill taken off). I believe too much cold water being mixed.

QUESTION. How do I increase temperature of water going under tiles?

Is the room up to temperature? And how how have you given it to heat up?

UFH doesn't or shouldn't have a hot floor. 32 degs is below body temperature so it will only feel tempid.

That 32 degrees on the manifold is the clue for me. I would check the blending valve on the manifold first and nudge it up in small steps, as it sounds like it is mixing in too much return water before the loops. Also compare the flow and return temperatures on a loop and make sure the actuators are actually lifting, because a stuck pin will leave a loop cold even when the pump is running. Tiles will still only feel mildly warm at normal UFH temperatures, so give it a good few hours after any change before judging it.

12 hours ago, JohnMo said:

Is the room up to temperature? And how how have you given it to heat up?

UFH doesn't or shouldn't have a hot floor. 32 degs is below body temperature so it will only feel tempid.

Thanks, l give it three hours. I have felt the tiles mildly warm before but tepid is with just above chilled tiles. The room temp is 19 and I have thermo set at 21. the water temp does go up to 36 but its inconsistent.

17 minutes ago, Adrian Clark said:

Thanks, l give it three hours. I have felt the tiles mildly warm before but tepid is with just above chilled tiles. The room temp is 19 and I have thermo set at 21. the water temp does go up to 36 but its inconsistent.

Depending on screed depth or floor buildup, warm up times can be way longer than 3 hours with UFH.

20 minutes ago, Adrian Clark said:

the water temp does go up to 36 but its inconsistent.

That sounds like your boiler is cycling, one of the issues with zoning central heating. Is this the only part of the heating system on? What is the rest of the heating system and how is it controlled?

More info you can provide the better

8 hours ago, JohnMo said:

Depending on screed depth or floor buildup, warm up times can be way longer than 3 hours with UFH.

That sounds like your boiler is cycling, one of the issues with zoning central heating. Is this the only part of the heating system on? What is the rest of the heating system and how is it controlled?

More info you can provide the better

This morning's situation. I checked the system which was flowing had been running for 2.5 hrs. Sequence of checks:

1. The ufh is the only zone on the two upstairs radiators are on a separate thermostat.

2. This morning the copper pipes were hot up to the mixing manifold.

3. The return and outbound manifolds were tepid as were the pipes going into the floor.

4. Water temperature 30 degrees.

5. Then the system clicked, stopped calling for hot water with the room temp at 20 degrees and thermo set at 21 degrees.

6. I turned the thermo up, see photo, it called for heat but the combi boiler did not respond (water ufh temperature dropped to 26 degrees).

7. I turned up the seperate radiator thermostat the boiler responded.

8. I observed the combi boiler heating system which consistently responds rapidly rises to the 53 degrees setting after gradually dropping to 43 degrees.

9. As I write the ufh water temp is 28 degrees with the system just incomprehensibly clicked off with room temp 20 degrees and thermo at 21 degrees. It then clicked back on. It seems haphazard.

Stevenlee is right about too much cold water being mixed. I dont know what a blending valve is (unless its the white knob i call a mixing valve).

(this help to figure out the problem is priceless I am grateful).

I wouldn't put too much faith in the calibration of that thermo head, a couple of degrees higher might sort it for you

Think your issue is more than setting the UFH flow temp.

With only 3 loops of UFH on, your boiler cannot get the heat away quick enough and goes in to self protection mode, switching off and letting the system cool for x minutes and try again. Easy anolagy is a kettle with below minimum water level and a full kettle. The full kettle has a nice controlled run, the kettle with too little water boils and doesn't trip off the element when it's hot. The boiler is seeing to little water and seeing a rapid rise in temperature and saying something not right I will stop.

So to get this all working well you need to look wider and at the whole CH system.

Still way more information needed

1. So assuming radiators elsewhere all with trvs? Yes or no, if no what exactly do you have?

2. How many thermostats do you have?

3. How many radiators per thermostat or are they all on TRVs?

4. What boiler do you have and it's size

5. How big is your house and how old is it

6. Anything else I have missed?

And to add to the above post, are you trying to heat just the UFH while doing these tests, or the radiators as well?

If just UFH and radiators are off, then it is indeed very likely the boiler is unhappy and shutting down. Try it with radiators running and UFH on at the same time, the radiator load should keep the boiler happy.

Turn up that big white dial on the left of the bottom manifold. That is what sets the temperature going into the UFH loops.

UFH does take a long time to warm up. Every year when we turn the heating on, later that same day SWMBO says "the heating's not working in the En-Suite" Next morning it is toasty warm and then stays warm with very little heat input.

Thank you. More information:

So assuming radiators elsewhere all with trvs? Yes. Only upstairs, See photos.

How many thermostats do you have? Two, the previous photo for the ufh and the one for the radiators, see photo.

How many radiators per thermostat or are they all on TRVs? One thermostat serves our two radiators, they are efficient.

What boiler do you have and it's size. Greenstar Heatslave II, see photo (eighteen months old)

How big is your house and how old is it. Small 2 bed cottage, roughly 40 sq metres footprint, 200 years old. Renovated with underfloor heating installed downstairs some time after 2009 (no paperwork discovered).

Anything else I have missed? When I do the tests I have only run the UFH.

27 minutes ago, ProDave said:

UFH does take a long time to warm up. Every year when we turn the heating on, later that same day SWMBO says "the heating's not working in the En-Suite" Next morning it is toasty warm and then stays warm with very little heat input.

We are about 24 hours from a coke start, tried doing setbacks once, and ended up switching the heat off at lunch time to get a night time set back. But restarting the heating about midnight to catch for the next morning. UFH is very slow, time scheduling is just a waste of time in my experience.

SWMBA must be kept warm 😃 I forgot, we also have this control unit.

From what I can see the minimum output of the boiler is about 10kW, which is pretty big based on what you have told us. Most likely a low heat loss in the depth of winter than you min modulation.

Your biggest issue is trying to run UFH on it's own. If you do you will just have the issues you are seeing.

I would simplify to get the whole system to run either on or off. The following will sound wrong to what people tell you.

To get everything to work, you need to turn down the boiler flow temperature, wind your radiator thermostat up so it doesn't interfere with heating for now.

When turning down boiler flow temperature you want the radiator rooms to slowly heat up so the radiators stay warm most the time. This will allow the UFH to get a continuous flow of heated water.

You will need the flow temp to about 15 degs above the UFH flow temp to give the UFH mixer some authority.

At a guess the CH flow temp will be set at 70 degs, turn this down to 50. Then switch your heating on with all thermostats set at 24 or higher. Leave the system to run all day - a job for a Saturday or Sunday. Assess how the room temps are,if your bedrooms get too hot bring down the flow temp a little if they are not warm enough add a couple degrees to the flow temperature. Also look at you UFH temp if room to cold turn the white knob up a little 1 Deg makes a big difference, opposite it rooms to hot.

Ideally deleted the radiator thermostat and put trvs on the radiators - ideally ones than never fully close down.

Your aim is not to have many timed on off periods, so have one or one for day and night, but run long and slow. You will most likely use way less oil than you do now, because the boiler will be happier and it will be in condensing mode all the time