Grant Vortex Condensing Combi 26 - (2006)

[kevint3]

Calling all Grant experts please!

Just moved to a house with a Grant Vortex Condensing Combi 26 (2006) with full underfloor heating.

The plot so far:

All was happy until cranking the heating up to 27 degrees, next day no hot water.
Figured out if the heating was calling for heat the hot water would work.

First thoughts were DHW plate heat exchanger or blend valve.

Auto vent valve replaced as seized (some black deposits came out), removed blend valve which was quite clean and put back on.

Hot water working again (weird), however now no heating if water store switched on and DHW pump constantly running.
If I turn off water store, DHW pump stopped immediately and CH pump starts.

Tested flow switch, pressure switch and both thermistors, all ok.

Now thinking PCB or back to my first though DHW plate heat exchanger maybe flow issue?

Please help as I am now at a loss.....

 

[Exedon]

DHW pump not shutting down 3 main causes.
Flow switch stuck open check with multimeter.
Non return valve on heating pump stuck open .
PCB fault
Exact model number would be useful Grant have made several different combi's.

 

[oilhead]

If you are getting flow but no hot water, is the primary pipework to the DHW ht Exch getting hot? If so, then the HtExch is suspect. If not, then your problem is with the control circuitry, so follow the comprehensive fault finding flow chart. Be sure to follow it in strict order, not bypassing a step that you 'know' is working.

 

[kevint3]

DHW pump not shutting down 3 main causes.
Flow switch stuck open check with multimeter.
Non return valve on heating pump stuck open .
PCB fault
Exact model number would be useful Grant have made several different combi's.

Hi, its a Grant Vortex Condensing Combi 26 (2006/2007 year)

Flow switch checks out fine.
Pressure switch checks out fine.
Both thermistors checked out fine.
Blend valve removed and refitted (hardly any limescale)

Since then I found a relay which controls the DHW pump had burn mark around contact.
Replaced this but no joy, DHW still running non stop therefore no heating.

Not checked non return valve yet, need to read up on procedure.

 

[kevint3]

If you are getting flow but no hot water, is the primary pipework to the DHW ht Exch getting hot? If so, then the HtExch is suspect. If not, then your problem is with the control circuitry, so follow the comprehensive fault finding flow chart. Be sure to follow it in strict order, not bypassing a step that you 'know' is working.

Hot water is working fine, keeps water store to correct temperature and burner stops but DHW pump carries on constantly. Therefore no heating.

 

[kevint3]

Hi, its a Grant Vortex Condensing Combi 26 (2006/2007 year)

Flow switch checks out fine.
Pressure switch checks out fine.
Both thermistors checked out fine.
Blend valve removed and refitted (hardly any limescale)

Since then I found a relay which controls the DHW pump had burn mark around contact.
Replaced this but no joy, DHW still running non stop therefore no heating.

Not checked non return valve yet, need to read up on procedure.

There are 2 non return valves one in CH direction and one in DHW direction (pump is next in line), turned boiler off, isolated cold mains feed and ran tap, tap stopped. (so I assume its not stuck open!)

Also rechecked flow switch by disconnecting, DHW pump carries on running.