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UFH fault


ProDave

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It's that time of year.  My turn to have an UFH fault.

 

This is in our old house, still owned by us and let. The problem is the downstairs UFH.  Here is the manifold:

 

20200130_111342.thumb.jpg.bc5ecda4a03d5e3a41b32ce1b6993c31.jpg

 

Flow and return come in from the left (the red and blue service valves) from an oil fired boiler.  The brass 3 port valve at the bottom left with the temperature gauge is the thermostatic blending valve. the adjusting handle is just out of shot of the bottom of the picture.

 

All the electrical controls seem to be working,  The UFH controller is calling for heat.  The motorised valve (mounted next to the boiler) is opening and is calling for heat from the boiler which is firing.  The UFH pump is circulating as it the main system boiler. the manifold actuators are opening and water circulating through the UFH pipes.

 

What is not happening is significant flow from the boiler.  the flow pipe into the red service valve is hot to the touch, but everything else on the manifold is cold to the touch and so is the return pipe from the blue service valve.  The temperature gauge is reading 20.

 

I am thinking it must be the blending valve is stuck in the "satisfied" position so not allowing heat in from the boiler and just recirculating what it has?  does that sound like a plausible failure?

 

If so does anyone recognise that blending valve?  the whole system came from Continental in about 2004 so I will fire off an email to them to see if they can supply a new valve but suspect it may be available somewhere else cheaper.

 

But I am seeking a sanity check from the forum before I continue the "fault find by substitution" method.

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While I await an answer from Continental, I have found this blending valve that looks right (it is the other way up in their photo) https://www.heatingcontrolsonline.co.uk/underfloor-heating-c-44.html/wet-underfloor-heating-c-44_49.html/underfloor-heating-mixing-valves-c-44_49_58.html/ufh-manifold-mixing-valve.html

 

They say it is is for "older John Guest and Polypipe manifolds"  Do you think mine is either of those?

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I was hoping for a positive diagnosis so I could order a part, then go and fit it.  I still don't have that confidence to make that decision.

 

So I think tomorrow I am going to go and do a partial drain down, and remove the blending valve.  That comes with additional complications as I then have to disconnect power from the manifold control box so I can then leave the system partly drained down and in a state that the rest of the heating can be operated.

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7 hours ago, ProDave said:

now have a part number and a cheaper price for this blending valve https://www.mepstock.co.uk/temp-cart.php

 

 

That seems to be somebody's cart with zero items in it but a total of £4961.67 (or their software is particularly flaky when the appropriate cookies aren't present). Anyway, not a blending valve.

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Try this link https://www.mepstock.co.uk/plumbing-supplies/polyplumb-pipes-and-fittings/polypipe-28mm-manifold-control-mixing-valve

 

I have found the same valve in 4 places so far. These are the cheapest and the only ones offering free postage as well.

 

The shopping cart had screwed up for me as well.  I would love to speak to the web designer and ask him what was the logic in deciding to empty the cart if you have not bought the item in a few hours?  They obviously don't understand consumer behaviour. The only way to find out the postage is put it in your cart, then you go and look for alternative suppliers before making up your mind,  It needs to stay there until you buy it or delete it.

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2 hours ago, ProDave said:

Try this link https://www.mepstock.co.uk/plumbing-supplies/polyplumb-pipes-and-fittings/polypipe-28mm-manifold-control-mixing-valve

 

I have found the same valve in 4 places so far. These are the cheapest and the only ones offering free postage as well.

 

The shopping cart had screwed up for me as well.  I would love to speak to the web designer and ask him what was the logic in deciding to empty the cart if you have not bought the item in a few hours?  They obviously don't understand consumer behaviour. The only way to find out the postage is put it in your cart, then you go and look for alternative suppliers before making up your mind,  It needs to stay there until you buy it or delete it.

I think I would be taking the valve out, stripping and inspecting it. It will operate with a waxstat capsule, the whole thing really is very very simple. I'd probably jam it on no blend, remove parts to disable it or similar, refit and if the system heats up you have your fix. Only run system like this temporarily but it proves your fault.

 

Water in a pan over the hob test for me if you suspect, and it almost certainly will be, the waxstat.

 

 

Edited by Carrerahill
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2 hours ago, ProDave said:

Try this link https://www.mepstock.co.uk/plumbing-supplies/polyplumb-pipes-and-fittings/polypipe-28mm-manifold-control-mixing-valve

 

I have found the same valve in 4 places so far. These are the cheapest and the only ones offering free postage as well.

 

The shopping cart had screwed up for me as well.  I would love to speak to the web designer and ask him what was the logic in deciding to empty the cart if you have not bought the item in a few hours?  They obviously don't understand consumer behaviour. The only way to find out the postage is put it in your cart, then you go and look for alternative suppliers before making up your mind,  It needs to stay there until you buy it or delete it.

This is obviously not the correct one, however, a bit of searching and you may find the right part:  https://www.showerdoc.com/grohe-avensys-wax-thermostat-element-00798000

 

Another failure more could be a rubber diaphragm type seal, however, normally these work on very reliable plunger type affairs and a small leak past isn't an issue. 

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3 minutes ago, Triassic said:

The blending valve simply allows cool return water to mix with the hot boiler water, so even if it’s stuck open or closed it shouldn’t stop hot water entering the system?

Of course it could, simply put yes, but it is basically an automatic valve which varies the flow from return or hot to create the ideal temp. If it was to completely isolate the hot intake side, which in the event that there was no demand and the manifolds were hot, it would just cycle the local water until demand dropped circuit temp.

Edited by Carrerahill
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Edit on my above post (2 up), it looks like you could drop the active parts from that valve by removing the collar under the temp adjustment without the need to remove anything from the system. Not only that, if you did need a new one, I would be tempted to leave the existing body and replace only the inner workings to save some faff.

Edited by Carrerahill
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12 minutes ago, Carrerahill said:

Edit on my above post (2 up), it looks like you could drop the active parts from that valve by removing the collar under the temp adjustment without the need to remove anything from the system. Not only that, if you did need a new one, I would be tempted to leave the existing body and replace only the inner workings to save some faff.

Thasnks.  I am going back there shortly so that will be my first line of attack.

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Right, I am back from my further diagnosis visit.

 

I took the bottom adjusting knob assembly off.

 

With that off, if I open the return service valve, water pours out.  If I open the flow service valve, water just trickles out.

 

To confirm it is not the actual flow pipe from the boiler blocked, I cracked open the nut on the output of the flow isolator and water poured out of that.

 

So that seems to confirm it is not accepting hot water flow in even when stone cold.

 

I could feel the cartridge but it's close to the floor and I could not see in and it was not inclined just to drop out so I aborted that.

 

I can't remove the complete assembly and leave it, as annoyingly one of the service valves does not shut off completely so would leave a drip drip drip with nothing to plug the holes left by the blending valve.

 

Off to order the replacement.

 

Oh and Continental just replied.  they no longer do that manifold, they can't supply spares, they suggest a new front end to the manifold with a different mixer and all the changes to the pipework to go with that. No thank you.

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  • 2 weeks later...

The new blending valve arrived today. So this afternoon I went and fitted it, and normal operation has been restored.

 

Time to dismantle the old one for a post mortem.

 

This is what comes out when you undo it:

 

UFH_1.thumb.jpg.0a80eaa85dabf32d85aa893befef470e.jpg

 

Note that it took some persuading to get the bits to come out.  I believe the central, rather black looking bit is supposed to slide up and down against that conical shaped spring. Well it was well and truly stuck.

 

This is that central bit, after a bit of a clean up

 

UFH_2.thumb.jpg.36af4b77dcfbdc1f198a4be6d485f290.jpg

 

In the recessed bit is a "pin"  This is what the adjusting spindle pushes on.  I believe this is the thermostatic bit and the pin is supposed to push out and expand as the cartridge heats up?  Well the pin just pushes in with almost no resistance all the way and heating up the cartridge makes no difference, so safe to say it's broken.

 

This is the top of the cartridge polished up a bit:

 

UFH_3.thumb.jpg.5b9f04c5e54c8d86808044d22061f0de.jpg

 

I can't see how to dismantle it any further, i.e how you separate the copper looking cartridge from the brass body?

 

Anyway stamped into the copper cartridge bit is a number around it's circumference:

 

0793 3F 123

 

As the number is around the circumference and all equally spaced, I might not have picked the right starting point for that number.

 

Anyone recognise it?  Any chance of getting a new cartridge to restore this one as a spare for the future?

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