Grant vortex pro external 36e poor hot water

[Nathan Smith]

Hi,

I’m new to the forum but thought I’d sign up to try and get some help with a customers boiler.

Bit of background on the boiler first. The house was renovated extensively with new bathrooms kitchen etc and the above boiler fitted 4 1/2 years ago approx, with no other work done inside or to the boiler since as far as I’ve been told.

I have recently become their regular plumber with anothe of their projects so am now looking after their boiler.

Beginning of March I got a text asking for boiler to be serviced because the hot water wasn’t lasting more than a minute.

Gave boiler a full service still poor hot water, so went through the MI fault finding as not to miss anything and drew a blank other than faulty heat exchanger.

I have had another installer with me on the job and have spoken to grant technical twice now and a grant rep twice who still can’t think of a solution.

When you turn on a hot tap the flow, demand and DHW pump light activate yet the boiler doesn’t fire even after 4+ mins. The flow of primary water into exchanger is too hot to touch yet the return out back to boiler starts too hot then goes cold as does the DHW pipe from exchanger to blending valve. If you turn the tap off the primary return heats back up to match the flow into the exchanger (have measured with thermometer). The store will heat up and become satisfied leaving only the power led lit. CH works fine.

So far myself and the other installer have done the following work. New heat exchanger, as advised by grant technical, check valve fitted on DHW pipe to property again as advised by Grant technical, both thermistors tested and changed, CH and DHW pumps swapped over to eliminate pump problem, return manifold pipe taken off to check for blockage, PCB taken from my own grant boiler and tried as to avoid cost of a new one, new blending valve fitted (guess at the possibility of a fault forcing cold back into the heat exchanger backwards)

Going out of my mind trying to fathom
It out and with the grant engineer for our area on leave for another week no hope of anyone other than another installer coming to have a look.

It could be something stupidly simple I’m missing or haven’t tried but with two of us now having worked at it we’re both stumped along with another guy I rang after grant giving me his number as he does warranty work for them.

Can anyone help me please as to what it could be or what I could check? It’s almost as if the flow rates through the taps are too high but the MI states 18lpm max and I’ve had readings from three taps one at 10 one at 8 and one around 5 because iso valve is closed down. Mains pressure has been tested at 4.5 bar ish and being in north cornwall we have soft water so don’t suffer from limescale.

I’m relatively new to the oil industry and have already decided I don’t like grants from my experiences with them.

Sorry for the essay but wanted to explain as much as I could to avoid answering the same questions.

Thanks
Nathan

 

[SimonG]

Dodgy mixer tap or shower.

 

[island fling]

I'm just commenting to remind myself to come back to this. I had the exact same fault & Grant technical asked me to call them when I found the fault.
First things first though, You should really have a pressure reducing valve on that cold, down to 2.5 - 3 bar. This was one thing i changed for sure.
Daft question but are the pumps getting power for sure? Defo pumping the correct way?
Racking my brain as I think as it was about a year ago I solved a similar issue. Obviously the store isn't dropping in temp hence why the burner isn't kicking in.
It will come to be but for now I cant think but it caused me a few days of lost time & a lot of heart ache I know that.

Regards
Island Fling.

Edit - assume pumps are as you have CH....
have you tried the test switch just out of chance?

 

[Nathan Smith]

I'm just commenting to remind myself to come back to this. I had the exact same fault & Grant technical asked me to call them when I found the fault.
First things first though, You should really have a pressure reducing valve on that cold, down to 2.5 - 3 bar. This was one thing i changed for sure.
Daft question but are the pumps getting power for sure? Defo pumping the correct way?
Racking my brain as I think as it was about a year ago I solved a similar issue. Obviously the store isn't dropping in temp hence why the burner isn't kicking in.
It will come to be but for now I cant think but it caused me a few days of lost time & a lot of heart ache I know that.

Regards
Island Fling.

Edit - assume pumps are as you have CH..
have you tried the test switch just out of chance?

I can’t remember if I have or not now to be honest I know I had trouble with the power switch when I serviced it and took a while to get it to switch on. I think I did flick the test switch but it just springs back and wont stay on.

Yes pumps are deffo working as they should as we swapped them over too.

 

[island fling]

I can’t remember if I have or not now to be honest I know I had trouble with the power switch when I serviced it and took a while to get it to switch on. I think I did flick the test switch but it just springs back and wont stay on.

Yes pumps are deffo working as they should as we swapped them over too.

It will just spring back but it will heat once I’m pretty sure on that model just allowing enough time for a service. Other models you could leave them on but I’m sure that caused dozens of callouts/call backs as the house was always roasting as the heating kept churning away.

 

[island fling]

Have you changed the PCB? I assume it’s the large one that does both heating & hot water. I just wish I could remember what it was I found to be the fault, I spoke to the customer this morning & they seem to think it was the non return valve.
Have you check/replaced the flow switch? Doesn’t cost much so a good process of elimination, I know it’s obviously kicking the pumps ect in but wouldn’t do any harm to try.

 

[Millsy 82]

Is there power going to the burner?

 

[Nathan Smith]

Have you changed the PCB? I assume it’s the large one that does both heating & hot water. I just wish I could remember what it was I found to be the fault, I spoke to the customer this morning & they seem to think it was the non return valve.
Have you check/replaced the flow switch? Doesn’t cost much so a good process of elimination, I know it’s obviously kicking the pumps ect in but wouldn’t do any harm to try.

Hi yes your correct it’s the big PCB. I stole mine from my boiler that I know is working and fitted and that made no difference at all.

Not changed the flow switch but grant technical said that if it’s turning the lights and pump on then it’s fine. Can always give it a go.

The Rep I spoke to said that it’s possible but unlikely that the non return valve on the pump could be faulty. Like I said that and the two gate valves are the only bits not changed.


I guess if it’s not opening fully it can’t keep up with the demand when drawing water but opens just enough to heat the store up whilst not water is being used.

 

[Nathan Smith]

Is there power going to the burner?

Yes the burner fires to heat the store and also do the CH but it doesn’t seem to fire when the tap is running as island fling said the store doesn’t seem to be dropping in temperature despite the return from heat exchanger to boiler going cold while drawing hot water.

 

[Gazzt]

Check the diverter valve, diverter valve diaphragm if fitted on that model.
Also found this on Grant manual

Store switch - Allows the primary store to be manually switched off if hot water is not required. With the switch set to OFF, the burner will not fire to maintain the water temperature in the store and the hot water (store) pump will not operate.
IMPORTANT: The boiler will not produce hot water.

 

[Nathan Smith]

Check the diverter valve, diverter valve diaphragm if fitted on that model.
Also found this on Grant manual

Store switch - Allows the primary store to be manually switched off if hot water is not required. With the switch set to OFF, the burner will not fire to maintain the water temperature in the store and the hot water (store) pump will not operate.
IMPORTANT: The boiler will not produce hot water.

This model doesn’t have a diverter valve. It’s all done with two separate pumps. Almost wish it did as that would more than likely be the case.

Also no on/timed/off switches on this one it’s all controlled externally. Hot water is on demand wired up permanently and heating is controlled by a nest went over all the wiring and checked with the electrician when he popped in one day while I was there.

 

[Millsy 82]

If the pump is coming on, its a new pump and the plate isn't getting hot it says to me 1 of two things blockage or air.

Is there a non return valve on the pump or is that just on heating pump. I would whip the plate out the pump out etc and make sure there is no blockages.

Also what pump have you put in? A wilo? I've had a new one that spun but the spindle was broken so the impeller didn't spin. So maybe try switching the heating and hotwater pumps over.

 

[Nathan Smith]

If the pump is coming on, its a new pump and the plate isn't getting hot it says to me 1 of two things blockage or air.

Is there a non return valve on the pump or is that just on heating pump. I would whip the plate out the pump out etc and make sure there is no blockages.

Also what pump have you put in? A wilo? I've had a new one that spun but the spindle was broken so the impeller didn't spin. So maybe try switching the heating and hotwater pumps over.

Not had a new pump, but have swapped the CH and DHW pumps over to test any fault. Brand new plate exchanger so unless it blocked after it was swapped? Return manifold has been removed and is all clear.

Yes there is a non return valve below the pump before the water enters the store. Only part I’ve not got involved with.

Have cracked all the nuts while it’s all been running to see if it’s air trapped but all let water out with no air.

 

[Gazzt]

Did you trace the fault

 

[Nathan Smith]

Did you trace the fault

No still no joy. Trying to find time amongst a busy schedule to spend on it is proving difficult, that and my supplier messing up my order for a non return valve.

Ordered one that will be here Thursday so going down to fit that and see if it’s that at fault. Theory being if it’s not opening fully it’s not allowing the flow through the heat exchanger quick enough to cope with the demand but withe no hot water being drawn off it cycles enough to satisfy the store.

 

[John.g]

Any update on a fix for the above?.

 

[Nathan Smith]

Any update on a fix for the above?.

Yes been meaning to post back in here.

Turned out to be the non return valve on the DHW pump. All though it moved, my guess was that due to the magnetite build up on it when it got hot it stuck and didn’t open fully. Put a new one on and it’s all working fine.

 

[WHPES]

Following. Any progress? I had this problem and found the water jacket was full of sludge. I cracked open all the plugs, disconnected the pipework and dangled a drain jetting hose inside. You wouldnt believe the sludge that came out

 

[Nathan Smith]

Following. Any progress? I had this problem and found the water jacket was full of sludge. I cracked open all the plugs, disconnected the pipework and dangled a drain jetting hose inside. You wouldnt believe the sludge that came out

Yes it was the non return valve on the bottom of the DHW pump. Was sticking when it got hot so put a new one on and problem solved