Question regarding connecting underfloor heating to existing system

[Steve2381]

Hello all

Well.. after a rogue builder left us in chaos... I am trying to pick up the pieces with zero funds...:banghead:

Underfloor heating manifold + pump is install and pressurised (has been for weeks) downstairs (about 3 metres directly below the boiler cupboard). That went in fine.

I have run a 22mm copper down from the airing cupboard (where the Performa System HE boiler and megaflow CL170 are installed).

My plan... correct me if I am wrong!....

Connect the 22mm copper to the boiler flow, somewhere where it splits into the existing electric heating and hot water valves.
This new 22mm feed then goes through a new 2 port 22mm valve and onto the underfloor heating manifold flow port.

The return port from the manifold, I planned to tap into the 22mm ground floor radiators return which passes right by the manifold. I established it was the return by letting the system go cold and then firing up the rads.... out of the two 22mm pipes, the one that got hot first would be the flow from the boiler. Therefore the other is return.
Is it OK to share the short 3 metre 22mm return run back up to the airing cupboard with the rads? They would connect together in the airing cupboard anyway before returning to the boiler.

The underfloor heating pump will be wired to run when the underfloor heating stat calls and also fire the boiler (I am a sparky - that bit is easy).

Another question. Getting in the airing cupboard now is madly tight. Would it be OK to tap off the boiler flow and fit the electric valve for the underfloor heating downstairs by the manifold instead? That will be about 3/4 metres away from the boiler at most. Getting the valve in the airing cupboard is going to be hell. Also, I imagine its best to have the valve below the point you tee off the boiler flow pipe and that may prove impossible in the cupboard.

Any other tips? I know to run it up slowly over a few days - increasing 5 deg a day or so from a start of 35 deg.

Thanks for any advice
Steve

 

[Howsie]

Welcome Steve!

I'd take a step or two back if I were you. Do you know if this rogue builder has specified and fitted the UFH pipes correctly?

 

[Steve2381]

Hi Howsie... I fitted the underfloor heating and the system came from a company who sent the required pipe/manifold etc - measured from the floor plan. I know it went in as it should. I pressurised it while he screeded and its held pressure fine.
We deleted several large radiators during the build so I think the system can cope OK (its a big boiler). Anyway... no funds to replace that!
I have been involved with many underfloor heating systems, I just have never actually connected them to the system before - so I was checking my limited knowledge (and yes.. little knowledge is dangerous!).

My real questions is whether its OK to have the 2 port control valve 3 metres away from the boiler (can't see why not) and if it is OK to share the ground floor return pipe (which is the same floor as the underfloor heating). There are only 3 other radiators on the ground floor using that 22mm return pipe anyway.

Thanks

 

[Howsie]

It should be but without seeing the system that comes with the usual caveats.

 

[Howsie]

If it isn't, you can always re plumb.

 

[Steve2381]

Ha... My thinking as well

Attached is an appallingly quick diagram if it helps.
My main worry is the water returning from the underfloor manifold will backflow around the ground floor radiator system if they are not on.

 

[Howsie]

You'll be fine.

 

[steadyon]

I'm no expert on UFH, but thought they normally ran at much lower temperatures than CH radiators. Is there a blending valve in with the manifold / UFH zone valve set up. If not your UFH temperature may well be too high.

 

[Steve2381]

I am no expert either Steadyon...

The manifold has its own blending thermostat and pump. It says in the installation manual to connect directly to the boiler flow/return and control the underfloor temps with the blending stat.

My super basic diagram doesn't include the blending stat. The manifold came pre-assembled with the blend valve, pump etc all fitted.

 

[dancinplumba]

dont forget your bypass which should be before all valves

 

[Steve2381]

Err... bypass? No bypass on my pretty plumbing diagram that came with the manifold.
This is a underfloor manifold added to an existing working system... won't their be a bypass on the existing system. I suppose it depends on what it bypasses!
Where does that go?

 

[Whn1]

There is a built in bypass I believe but it's very small bore, if I can remember correctly.

 

[dancinplumba]

you need one between F an R pipes on boiler, ignore the fact there is one in boiler, it is inadequate.
When ALL valves closed where does heated water go ?

 

[Steve2381]

Err.. where ever it has for the last 5 years! So adding a manifold to the boiler means I need a bypass, even though the system has worked fine as it is without one so far?
There is absolutely no way I can get to the flow and return under the boiler (hence the connection the the flow pipe at a different location. The Megaflow has been mounted directly under the boiler blocking access to the pipes out of the boiler totally (yes - stupid but not by me).

The boiler is a Potterton Performa System HE. It does have an internal bypass, so I expect the original plumber is relying on that

 

[Whn1]

They will work with the internal bypass but what dancin is saying is its reccomended/a lot better for your boiler to have an automatic bypass fitted before the first motorised valve. You have to access this point anyway to tap in for the primary flow to your manifold.

 

[Steve2381]

OK. Yes I can 'just' reach the flow where it leaves the boiler and splits to the original hot water and central heating valve. However, as I cannot access the return at all (totally hidden from view), I am not going to be able to connect the other side of the loop.
I only just managed to fiddle a new 22mm out of the airing cupboard down to the manifold to get me a new separate flow pipe for the under floor manifold.

I suppose you could jump across between the flow before it enters the under floor heating valve and then tee into the return pipe downstairs? (see attached updated sketch).

What is inside a bypass valve anyway? I am assuming a simple temperature controlled valve that lets water over a certain temp through. What temp would this valve normally be set at?

OK.. Edit post: Its a pressure valve then ... set to 0.2bar.

 

[Steve2381]

Ever wish you hadn't started something?

OK.. all in.. working sort of fine. Fitted a bypass - just in case. Underfloor heating was on and away (set low) last night.

This morning... one of the flow meters on the manifold is stuck down (a light tap doesn't free it). Any ideas?

Also, and slightly more concerning is the boiler is now humming (sounds like a light airplane) when the central heating is selected (the radiators). Any ideas on that?

 

[Howsie]

Change the flow meter or use pipe thermometers to get the balance right.

Boilers usually hum a little.

 

[Steve2381]

OK. De-pressurised the manifold - TINY bit of crap stuck in the flow meter.

What should the bypass be set at? Its factory set at 0.2 (which doesn't seem very high). I have moved it to 0.4 and possibly imagining things.... but it sounds quieter.

Any suggestions?

OK EDIT...

The humming from the boiler is getting louder and louder. What the hell is that.
Only seems to do it on the central heating

 

[Howsie]

Bypass depends on the installation setup.

Boiler could have air in it or could be going wrong. Who knows...

 

[Steve2381]

Well its a vibration of some sort. I thought slowing up the underfloor heating pump may help... and I thought it did for a while.
But then the hum inside the boiler slowly returns over 5 minutes... getting louder and louder. Instantly stops when you turn off the central heating on the programmer.

Is the small black knob built into the top of the boiler pump a manual or automatic air valve? Although surely the noise would be on the hot water as well if it was air.

This is turning into a really bad week

 

[Steve2381]

OK. Just to keep the thread updated (why I hear you ask!)

Slowed the underfloor heating pump to speed 2. Noise seems to have slowly disappeared. Not going to say its gone, but currently.... running quiet.

Fingers crossed. Thanks for all the advice guys

 

[Howsie]

Sounds like the UFH is pumping against the boiler. Have you connected them the right way around?

 

[Steve2381]

Yep - pump on manifold is correct. All works fine. Underfloor heating is working fine.
Its just every so often... sounds like a light airplane passing over. Certainly coming from the boiler and doesn't sound like the pump to me.

I have set the bypass valve I installed to 0.5. Quite high I expect, but set lower than that seems to make it worse. There is one in the boiler apparently anyway.

The underfloor heating pump is currently running set on speed 2. There is no speed adjustment (that I can see) on the boiler pump - not that I would change it.
I thought perhaps the underfloor pump was interfering with the boiler pump - making it noisy. The underfloor heating seems to work fine on speed 2, so I don't think that is an issue.

All radiators are bled, so not sure what the noise is.

Its all running now - and quiet. Has been for the last half hour. Perhaps it is just air?

 

[Steve2381]

Mmm... its run all afternoon just fine. Then tonight when the CH came on, it sounded like a Boeing coming in to land. The 'hum' just got louder and louder.

No hot water issues (that I can see). Radiators are lovely and hot. Underfloor manifold/floor seems to be working fine.

Blocked heat exchanger? Perhaps draining down has dislodged some crap in the pipes (I did flush through the pipes as best I could - fairly brown but not sludgy). I was going to put inhibitor in the CH system, but not until I know its all working fine.

Anywhere else muck could be trapped, and is this something I can do... or after all my efforts, am I going to have to admit defeat and borrow money for a plumber?

Edit... Is Fernox boiler silencer concentrate (the one you add via a rad vent with a mastic gun) any good?
Fernox stuff is usually quality. Wondered if this was worth a shot.