Underfloor heating, I've done the donkey work testing, can you diagnose

[Mike Jones Amber Hill]

ok, so I have a underfloor heating manifold with 11 ports (see pic)

Rooms struggle to warm up. Think I know why, here's what I've tested:
1. Pressure expansion tank in garage 2 bar - ok
2. Boiler working, water hot - ok
3. Thermostats calling for heat and actuators respond - ok
4. Flow: all meters were totally corroded, had to bin and put new ones (see pic)
5. New flow meters show minimal flow (0.5 - 1 lt pm)
6. Checked valves, opened all fully, no stuck pins - no change to flow
7. Flushed system with garden hose, line by line, no air locks

So, it seemed flow was the problem. To test this I closed the return valve and all actuators, and opened the drain valve on the pipe directly from the pump (I.e. flow side)This showed me the pump was delivering 7lt pm, and the water was piping hot (steam off the bucket).

To check the rate the water was going through the underfloor heating pipes, I closed the drain valve on the flow side, and opened one actuator and opened the drain valve on the return side, and closed the return valve, so water would only flow through the underfloor pipe and then through the drain. This showed 7lts pm was flowing through, so same as the flow side, I.e. No blockage.

THE ANSWER?
Is the problem just that the system is only getting 7lts pm? I'm thinking that at an average of 1.5 lts pm, per port/line, it might need a total input flow rate from the pump of around 15-20 lts per minute? If this is correct, is the pump the problem?

PUMPS
there's a pump directly on the manifold (standard Grundfos - see picture), and there's a pump in the garage (looks higher tech - see pic), and not sure how these may support each other?

I'm wondering if the corrosion on the flow meters might suggest other components could be corroded and not working properly. The pump sound normal. I have unscrewed the valve and no air in it.

CAN YOU DIAGNOSE THE PROBLEM??

Mike

 

[oz-plumber]

Not enough flow.

Either mixing valve, pump or both.
If the flow meters were as bad as that, I would change the mixing valve. Undo the screw on the pump and see if you can stop the spindle with screwdriver, by pushing gently - if so, replace pump capacitor ( if available ) or replace pump

 

[Mike Jones Amber Hill]

Thanks.

I'll try the pump.

What causes the flow meters to go like this (all black and seizure up (the pins are fixed solid, can't even move with pliers) and is there a way I can avoid it in future? An additive?

Mike

 

[999]

Yeap, add plenty of inhibitor to stop it happening again

 

[Chalked]

You need a biocide inhibitor, in underfloor heating.
Your problem will most likely be the mixing valve.

 

[Sharp Point]

The image isn’t the clearest, but are those two 15mm coming down to feed the manifold or been tee’d into the 22mm circs and go off and feed a radiator?

 

[Mike Jones Amber Hill]

The image isn’t the clearest, but are those two 15mm coming down to feed the manifold or been tee’d into the 22mm circs and go off and feed a radiator?

Yes, this manifold is on the first floor. We have a loft room above, which we wanted a radiator in, so teed off for this, I think the plumber used two thumb valves that were sitting there ie took these away and used for the 15mm pipe connection. You can see where - it's the two 'u' bend 15mm pipes, scorch mark behind the left one. Currently this radiator and controller are both off, so don't think it is causing the problem by, say, drawing flow, but open to guidance.

I have attached better pictures of that bit.

And here's a really dumb question: how do I get the biocide inhibitor into the system??

Mike

 

[Mike Jones Amber Hill]

And just to mention, unscrewed the cap on the grundfos pump, applied some pressure to the spindle with a screwdriver, and it made no difference even when pressed quire hard, so the pump seems to be turning strongly.

 

[999]

I use a injector like this one in the photo

 

[Mike Jones Amber Hill]

It's not cheap, the biocide inhibitor. How much would I need? To give you and idea, the pipes are covering about 1400sq ft from the 11 port manifold, and there is another 11 port with same sq ft on ground floor. Only looking for a best guess, e.g. Is it 0.5 lt, 5lt to 50lt!

 

[Mike Jones Amber Hill]

Been googling, looks like I don't need gallons! In terms of getting it in, as I have a rad on the system in the loft, thinking easiest way is bleed off a bit from this, unscrew blanking nut a fill via this with screw fix £3 filling 'kit' which is really just a screw thread for the bottle and 3inches of hose pipe, but looks like it would do the job.

Re the mixer valve, I'm guessing the theory is that this is furred up like the flow meters where, which I assume means it is stuck. How does this result in low flow? It is currently set to max, and the water coming out is steaming in a bucket, so it's probably also running hotter than it needs to, which is expensive. It feels like I am in a battle with this system, it's big and complicated - I miss the old house radiators, never had to look at them once!!