UFH pipes not hot enough

So after about 15 mins with both CH and UFH on, I have been by the boiler and it keeps going from S.2 to S.4 to S.7 which is not what it was doing before when just the CH was on.

D.40 rapidly climbs to 68 when the boiler is firing and d.41 is 38 when S.7 kicks in and the boiler stops.

Both the UFH flow meters show 0, all the pipes around the manifold are cold but the UFH pump is on
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@Johntheo5 - the zone valve for the UFH is open so don't understand why the UFH is not turning on unless when the engineer power flushed the boiler pipes, this has an effect
@Johntheo5 - I have turned off the UFH as I am concerned I might be causing damage to it. The UFH pump is on but is cold too.

I have attached some photos of the UFH while the UFH system was on


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OK that's fine .
Can you switch off the UFH, switch on the CH only and if boiler runs "normally" then check and see if the Grundfos is running, then take a few more readings, same as before, d.40 & d.41.
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thanks @Johntheo5. I now have just the CH running but the boiler is continuing to cycle from S2 --> S4 --> S7 at 7kw

When the boiler shows S4, d.40 rapidly goes up to 67 before S7 kicks in. d.41 stays at 37

What has changed? Before when only the CH was ON, the boiler was staying at s.4 and d.40 was hovering around 63-64 with d.41 at 45
There's definitely a circulation problem but where to start. the status parameters are very easy to interpret.
S2 is pump start, S4 is boiler ignition, then because little or no circulation, d.40 (flow temp) shoots up and the dT, d.40p-d.41 hits 30, boiler shuts down and S7, pump overruns for a time to cool the boiler down, cycle then re STARTS with S2 PUMP START..
thanks @Johntheo5 but before I turned on the UFH, the boiler was not cycling through S2 --> S4 --> S7, and the boiler happily stayed at S4. Has, by turning on the UFH, caused some poor circulation within the Grundfos pump/CH system?

I am now really baffled :(. I have now turned off the CH just to let things settle down a bit
@Johntheo5 - I have attached some photos.

- 2 photos showing the boiler in the garage and the expansion vessel gauge
- hot water zone valve (labelled in yellow with the number 1). Within this photo, the 2 white pipes at the front are coming from the UFH manaifold
- zones valves - the one labelled '2' in yellow is for the UFH, the one labelled '3' in yellow is for the CH
- 3 photos showing pipework around the pump
- photo of pump showing upwards arrow on pump (circled in yellow)


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Will have to start somewhere, you might try and answer the queries in the attached, it is very important to try and establish that the E.vessel is tied in to the boiler Flow Pipe or not and before the circ pump suction.

Has the magfilter been cleaned recently?.


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Thanks @Johntheo5. I will try to answer some of your queries on the attached tomorrow where I can.

My boiler is covered by British Gas and they carried out an annual service on 26/9/22 which included cleaning out the magnacleen.

From the attached, I’m 99% certain that the boiler flow pipe is the one above the boiler on the extreme left.

On the pressure gauge, I will check but I do not believe the gauge rises when the system heats up
It certainly should rise, give it a judicious tap of a spanner at its side to see does it fall/rise to its real pressure.

See if the E.vessel is tied in here somewhere.
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