pipework query, pump feeding pump?

[christhescott]

Hi, we have an oil boiler which feeds HW, rads, and two UFH heating circuits using 4 zone valves and 2 pumps. Would anyone have a look at the photo and tell me if its right that the green pump has to be on to feed the UFH mix pump? Could the UFH pump have been teed in parallel with the green pump? I was having a look at the pipework and was surprised that the green pump was on when the Radiators and HW were off. The system works but seem to struggle when both the radiators and UFH need to heat up at the same time (mornings)

Thanks

 

[SJB060685]

Its hard to make everything out due to the close up photo. The green pump is the system pump which will circulate from the boiler and around the circuits and will be energised whenever a zone is falling for heat. Each UFH manifold should have its own circulating pump.
Has the system always struggled when both are on in the morning, or only recently?
What output is the boiler? And what is the load of each circuit?

 

[SimonG]

Aye, picture further out needed. What's the motorised valve for at the bottom of pic? There doesn't seem to be a motorised valve for the under floor.

 

[christhescott]

Its only recently I've noticed it struggling but it has been cold this past week and the radiators have been on constantly because we have a new-born in the house. The boiler is a warmflow and says 70/90. There are 4 single radiators upstairs and 1 double. The UFH areas are about 20sqm and 12 sqm though the smaller one doesn't get used.

 

[SJB060685]

In the colder weather the radiators need more power to achieve the same room temperature. Its entirely possible your system has been designed at the wrong outside temperature and lacking the boiler output to meet the demands in this cold weather, or the boiler output is not enough. You could also have a system pump flow rate problem, where by the UFH is drawing its design flow rate leaving less than required for the radiators, which would obviously leave the emitters (radiators) struggling to stay warm. Increasing the pump setting will increase the pump head and flow rates and could suffice, however this could throw the boiler delta t out and may result in hydronic separation or a buffer being the answer.
Is it a condensing boiler? Do you have any idea of the circuit loads?

 

[exedon2]

As a quick workaround you should have some sort of programmable thermostat on underfloor area just time it on say 90min earlier than rest of heating . Also what backset temperature is that thermostat set at?