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UFH: All stats calling for heat, no pump

Postby joshf1 » Fri Dec 03, 2021 11:11 am

I've had the system flushed and a few sticky pin valves replaced to attempt to rectify the problem of insufficient hot water flow round the floors. After all this it still seemed to lose too much heat on return. The only obvious issue was the Grundfos pump shutting off despite all thermostats on the pump and rooms set to max, but the engineer stated this wouldn't have been the problem as the pump would either work, or it wouldn't. Except now it doesn't at all! No light, boiler not firing. All room thermostats still requesting heat as indicated on the wiring centre.

As a layman is there any way for me override other controls to test the pump? Would setting it to mode III - 'manual' keep it on?
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Postby stoneyboy » Sat Dec 04, 2021 5:44 pm

Hi joshf1,
It is likely that somewhere in your system there are motorised valves, try and locate them and use the manual lever on them to check if they are the issue.
Regards, S.
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Postby ericmark » Mon Dec 06, 2021 7:03 am

Most underfloor heating has two thermostats in some form, one to see if room need heat, the other to limit floor temperature, the latter varies in the way it works, but idea is floor should not exceed around 27 deg C.

Often the water in the floor has its own circulating pump and the water circulates and when the temperature drops below the limit more hot water is added.

It is not one system fit all, so impossible to say if even a fault without knowing set up.

There is some debate over UFH, with gas and oil the normal was UFH controls back ground heat but radiators top this up, mainly due to response time with UFH, you want if the sun comes out for heating to reduce quick to stop over heating, and also for heating to turn down when not home then return quickly to required temperature, hard for UFH to respond fast enough.

However with heat pumps the cooler the circulating water the more efficient they work, so heating water to 60 degs C only to be then cooled to 30 degs before most of it being used seems a little silly, so there has been a move to 24/7 heating at a set rate and not a programmed temperature changing through the day.

This again means no standard set-up, and the heating and ventilating has become a job for an engineer, i.e. some one with a University education as it is becoming so complex.
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Postby joshf1 » Mon Dec 06, 2021 8:35 pm

stoneyboy wrote:Hi joshf1,
It is likely that somewhere in your system there are motorised valves, try and locate them and use the manual lever on them to check if they are the issue.
Regards, S.


So currently, after resetting the boiler, the valves on the manifold do as requested and pop up and I now have good hot water flowing round the floors and have managed to get 50 degrees from the return from one room, within 10 mins. Then the boiler shuts off but rooms stats still call for heat.

Previously the valves were off, as I'd turned the system off, but before resetting nothing was happening, even from the boiler. Now the boiler has stopped firing but valves are still open.

The whole time there was no light or sound from the pump but obviously water was still going through it.

Is this my boiler shutting off because it's doing all the work to get the water round?
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Postby joshf1 » Mon Dec 06, 2021 9:09 pm

Here's the setup and rough idea of the temperature as pressure readings. Still high an hour on but gradually cooling water under the floor is no use! Note stats still calling for hear and valves still open. Which is the mix to the cold? Could I turn my boiler up and that down so the boiler isn't getting too high a temp on return?

https://pasteboard.co/gunDmtdmBtg8.jpg
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Postby ericmark » Tue Dec 07, 2021 3:57 pm

The water needs to circulate or you get cold spots, so valves are likely open, but UFH is complex, it is not like radiators where 95% follow a standard layout.

This is why the guys who install it are called engineers, and also why repairs are expensive.

The basic thing is if you want UFH you need to pay for some one to fix it. The hypocaust has been around for a long time [attachment=0]hypocaust.jpg[/attachment] there is a reason why we stopped using it, it cost too much to maintain, be it slaves or tradesman it costs.
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