Worcester HiFlow 400 Boiler Issue

[Johntheo5]

Can you send on a link please to your boiler.

The boiler flow & return temps and the UFH flow & return temps will only be the same if the boiler flow temp and the required UFH flow temps are the same, generally, the boiler may have a flow temp of say 65C but the UFH may only require a flow temp of 45C (to prevent damage to floor covering etc), a UFH dT of ~ 6C to 10C, with 8C would be fairly typical, so you now have a UFH with flow/return temps of 45C/37C and a boiler with flow/return temps of 65C/37C, which means that the boiler flowrate is only, (45-37)/(65-37), 28.57% of the UFH flowrate, if the UFH heat output is say 9kw then its flowrate will be, 9*860/60/(45-37), 16.13LPM and the boiler flow rate will be 16.13*28.57%, 4.61LPM, this boiler flow rate of 4.61LPM at 65C will mix with 11.52LPM of recirculated flow at 37C (via the TMV&manifold pump) to give the required 16.13LPM at a mixed flow temp of 45C. Some boilers won't tolerate a dT of 28C so some form of by pass may be required to reduce the dT to ~ 25C, however, this isn't your problem since the boiler runs quite happily on UFH only. Based on the above, then the required boiler flowrate is very low at 4.61LPM or so BUT with a very high dT of, (65C-37C), 28C.

 

[hgrdkx]

A029620756043 is the serial number.

This is the manual I have been using and the one I can find most relevant, seems to match the wiring etc on the boiler:

https://www.acwilgar.co.uk/Boiler-Manual-PDF/Worcester%20Bosch/HIGHFLOW%20400%20RSF%20GCNo.47-311-18.pdf

The UFH has a control rotary dial for the temperature. Can be set from 40 to 65*/max I believe. Thanks for the info, I understand but agree, don't feel it is relevant. As with UFH has a flow + return isolator valves, with both closed and UFH isolated, rad valve open we still have an issue.

 

[Johntheo5]

Are you running the Boiler at the same flow temperature as the UFH flow temperature??, if so, then yes, irrelevant, as the the flow rate demand for 9kw of CH with a dT of 8C will be exactly the same as a 9kw demand of UFH with a dT of 8C, both will require a boiler flow rate of 16.13LPM.

 

[Johntheo5]

A029620756043 is the serial number.

This is the manual I have been using and the one I can find most relevant, seems to match the wiring etc on the boiler:

https://www.acwilgar.co.uk/Boiler-Manual-PDF/Worcester%20Bosch/HIGHFLOW%20400%20RSF%20GCNo.47-311-18.pdf

The UFH has a control rotary dial for the temperature. Can be set from 40 to 65*/max I believe. Thanks for the info, I understand but agree, don't feel it is relevant. As with UFH has a flow + return isolator valves, with both closed and UFH isolated, rad valve open we still have an issue.

Any update on the issue?.