Any Wet Underfloor Heating Experts?

[Andy Spencer]

Hi all

We have a wet underfloor heating system in a single storey downstairs extension. 2 circuits in one large floor. 6 years old and been brilliant so far. However recently in the cold weather I've noticed its just not working too well. Read up on some common faults and bled it over the weekend (no air), checked pump working (fine) and took the mixing valve off and cleared it of crud (yes there was quite a bit in it).

What's strange is that even with the two flow control valves/meters on the hot manifold fully open, I can't get any more than 1l/min flow rate through them, unless I close the mixing valve, where they jump up to about 4l/s (closed loop circuit). If I close one I can get about 1.5 to 2 l/min in the one circuit with mixing valve open. Therefore I think the issue might still be with the mixing valve. It cleaned up nicely though and seemed to flow, I also flushed out the hot central heating boiler water feed to it in a bowl until it ran clear.

Unfortunately I haven't monitored flow rates historically when it was running fine and understand that about 1.5 to 2l/min is ideal.

I still get a 45 deg C feed to the hot manifold and exit pipes are slightly warm, about 30 degrees, but I just don't think I'm getting adequate flow to warm the screed slab, as it doesn't feel warm to the touch as its done in previous years.

 

Any ideas welcomed and many thanks

Andy

[Guest outtolunch]

have you taken the pump head off its base to check the impeller they can come apart and will still pump but with reduced flow and they can also crud up a lot

[neil's]

Hi Andy,

Have you checked that your 2 port control valves fully opening up on the manifold on temperature demand. also have you got all your TRV fully open on your radiator circuits as this will starve you manifold if not balanced out correctly?

[BigLee]

Its all greek to me

[fry61]

Its all greek to me

ROMAN---- I think underfloor heating is down to the romans, the greeks just carved pretty friezes on the top of walls.

[Andy Spencer]

have you taken the pump head off its base to check the impeller they can come apart and will still pump but with reduced flow and they can also crud up a lot

No I haven't. Good call. Will take a look at that tonight. many thanks

[Andy Spencer]

Hi Andy,

Have you checked that your 2 port control valves fully opening up on the manifold on temperature demand. also have you got all your TRV fully open on your radiator circuits as this will starve you manifold if not balanced out correctly?

Another good point - I hadn't realised this could be the case. We've been running the heating for quite long periods with the TRV's set medium to low to try and reduce internal temperature fluctuations. I've got a good hot feed to the underfloor manifold when boiler is on, but will open up some TRV's to see if I can improve flow rate through the underfloor manifold valves.

Hope that I don't have to let other rooms get scorching and waste heat just to maintain flow rate in the underfloor system. Counter productive. I think I'll give the system a good flush out and clean all valves as well.

Cheers for the advice.

[Longboarder]

TRV's are just a room temperature control. On the other end of each rad there is a balance valve which controls flow through each rad. Setting up the system these balance valves are used to restrict max flow through any rad and ensure adequate flow to all the rads. You underfloor heating should be on a zone of its own but may not be. As it used to work fine then I assume that the system had adequate resources. So you need to be looking at what has reduced these. Overall flow loss or balance change diverting flow away from the underfloor or loss of heating capacity. I'm guessing the boiler is still fine so it's effective flow loss through the underfloor zone.

Have you been fiddling with the balance valves on the rads? Opening them up. That would divert flow away from the underfloor and to the rads. Has the pump lost efficiency? Did the system have inhibitor in it? Has the system furred up?

First I would de-scale and flush the system and then add inhibitor. If that doesn't sort it remove and strip and clean the pump. If that doesn't sort it then a central heating expert to re-balance the system.

 

Nigel

 

ps Graham (gdc) is a CH engineer and may be able to advise if you pm him.

pps Opening up the TRV's will reduce flow (or do nothing) to the underfloor heating. Closing them slightly might increase flow to the underfloor but it's not the right way to do it and as you say will change the temperature in the rest of the house.

[neil's]

Andy

i think you got the wrong end of the stick mate opening the TRVs to your rads will in fact will drop the volume to your manifold as stated by Nigel if you close them down you will be able to force water to your manifold, either through a lock shield valve or your TRV valve. As Nigel states it is a room temperature device but will also reduce volume, as the orifce inside the valve reduces so does the volume of water coming out.

You said the mixing valve was full of debris. check your 2 zone valve these to will no doubt be full of debris and need cleaning out.also. if you take the actuators of the valve body and pump the pin up and down this some time frees up the debris sat behind the valve seats. most 2 port valve have a low KV value and will only allow small volumes of water through them. the smaller the KV value the smaller the internal orifice of the valve body prone to get blocked up easily.. This tend to happen when you have low flow areas such as under floor heating system which do not get used all year round. the sediment settles in the low points of the system and and when they get turn on the water pick up the the sediment in the water and become in suspension and get stuck behind the valve seats and reduce flow rate. In that case you will need to back flush your under floor pipe work to remove the settle sediment within the pipe. don,t forward flush through the system as this will again get stuck in your control valves or you could remove them for this Is there any binder points on your system you could take a pressure drop across the manifold. if your getting 4 l/m ish closed circuit it will not be your integral pump, it would suggest a return issue to your main pipework / manifold something blocked / / not fully open/ controlling. has the manifold got a internal stat and what is it set to? or has this just been connected directly to your central heating system. if this is the case once the room stat is satisfied the boiler will switch off before all area are satisfied (hot) if internal stat is fitted More than this will control your mixing valve and open and close the valve and inject heat in as required and then will close when return temperature is satisfied. Its a process of elimination. By closing some TRV this will force increase the volume of water to the manifold the least favored circuit to help the process of elimination. once this is done check that the actuator head has driven the control valve fully open usually pin down on 2 port valves and pin up on 3 and 4 ports but can vary, if not you can manually depress the pin your self and hold it there for a while and see if that has an effect on the zone circuits temp. if no luck with that do the same with each zone control one at a time and see if volume increase or temperature increase on the return pipe.

[Andy Spencer]

Dear all

Thanks for your help and advice. I've sorted the problem - a combination of Furnox F3 in the system for a few days, a reverse flush out, cleaning of all valves (inc a full dismantle and clean of mixing valve) and pump impellor now gives me a flowrate of up to 3l/min (set it down to just over 2). Floor has warmed up nicely over the weekend so much relief from the cold!

Once again many thanks

[stevedohc2b]

I would fit one of these http://www.adeysolutions.co.uk/mcp_howitworks.asp

 

should help keep system clean

 

stephen