Grant Vortex pro 21 Oil Boiler Central Heating Issue

[markio123]

Boiler is a Grant Vortex Pro 21, installed around 6 years ago.

When Central Heating is demanded from the thermostat the CH pump will come on for a couple of minutes say and then the CH pump is switched off and the DHW pumps starts, the flow light is not lit, this cycle continues varyingly. As a result the CH pump is off more that it is on and the radiators do not get hot at the bottom. This issue has existed for quite some time, say since last winter.

The boiler had its annual service last week but the engineer could not figure out a solution to this problem and said he would speak to Grant directly. It was suggested by Grant that the problem was either one of the thermistors (store and flow) or the control PCB as a last resort. It made sense to purchase all 3 as a package from a cost perspective. The new parts were fitted by myself and the same problem persists. The removed thermistors didn't look in great condition, the wires where they were inserted had hardened, maybe that is normal?

I got a new Hive for Christmas that could control hot water and CH as I want to turn off the Hot water at night and most of the day to save burning oil unnecessarily. I fitted the new hive and have now discovered that if the hot water is switched off then the central heating works as the CH pump stays on continuously when demand is there and the rads all got hot at the bottom as they should.

So it seems that demand is being created by the DHW side and turning off the CH pump. My house has solid walls and floors and all pipework for the heating is 95% exposed so I'm pretty sure there are no water leaks creating the demand, neither are any taps or showers dripping.

I don't have an issue having the engineer back again but it seems to me he'll just be scratching his head once more.

Hot water always works fine.
I'm at a loss so any input greatly appreciated. Thank you.

 

[Exedon]

Like all combi's your boiler is hot water priority
The heating will not work if there is a hot water demand via the flow switch or the heat store is not up to temperature.
Some clear pictures of your board would be useful as there are several ways it can be wired.
Have you got a multimeter and are competent to use it?
Are rocker switches on front panel correctly set?

 

[markio123]

Exedon, Thank you for your reply. Please see below a picture of the PCB. Yes I understand that something is driving the demand for the hot water and hence the CH pump stops running. Of note is that demand for the DHW when the CH is heating is off is not apparent unless it just a quick blast to warm the store up, but if there CH demand the DHW is demanded much more (hope that makes sense!)

The second picture is showing when I have the CH heating demand on and the CH pump has stopped.
With regards to switches there is a Boiler ON/OFF and a service switch. The service switch is in the off position.
I have a multimeter and I am competent at using it

 

[snb1]

that picture shows that the boiler has the hot water tap on somewhere or the flow switch is on the way out. pull out the plug on connection 13/14 and see if demand light turns out. If so and your heating then works fine you have found the problem.

you would alos benefit raising the pressure up to 1.0 bar as it's close to the low pressure switch activating

 

[markio123]

snb1
I'll try that and see what happens, I thought that if a hot water tap was on somewhere then the 'flow' light would be on? Anyway there definetly no hot water tap on when I took the picture.

The boiler was serviced last week and I was assured that the pressure was set to 1 bar, so on top of this issue I'm loosing pressure somewhere.

It's dark now and a bit rainy on and off so maybe best left till tomorrow for me to look at pulling the flow switch connector.

 

[snb1]

snb1
I'll try that and see what happens, I thought that if a hot water tap was on somewhere then the 'flow' light would be on? Anyway there definetly no hot water tap on when I took the picture.

The boiler was serviced last week and I was assured that the pressure was set to 1 bar, so on top of this issue I'm loosing pressure somewhere.

It's dark now and a bit rainy on and off so maybe best left till tomorrow for me to look at pulling the flow switch connector.

sorry didn't read it correctly, might have been still sobering up!

 

[snb1]

Check that hot water pump is spinning.
check that all the air is out of the circuits. ( double check the manual air vent with the system turned off) make sure the auto air vents work as well
make sure system pressure is at 1.0 bar.
check that the flow ( grey cable ) and store ( black shroud) thermistors are in the correct locations
Most common cause is air in the top of exchanger

 

[markio123]

snb1

I just had a look and didn't like what I found!

The pressure this morning was not far off zero.

There is a leak coming from the pressure switch, if I touch the plastic on the switch I get a mild electric shock if the boiler is running, it looks like its been leaking for some time as its all a bit crusty.

The manual air vent top (white cap) was completely off and was laying inside the boiler, I screwed this back on and pressurised to one bar. It looks like when it was serviced he removed the cap and forgot to put it back on, it was serviced about 2 weeks ago.

The 2 AAV's also look a bit crusty.

So as it seems I'll have to drain the boiler down in order to change the pressure switch, do I also change the AAV's at the same time as they're
not too expensive? Would the leaking switch explain the issue with the CH pump switching off because of store demand?

Thanks.

Pics below.

 

[Exedon]

No need to change pressure switch just remove 1/4 plug to blank then put link wire on board.
They have not been fitted by Grant for several years are a known cause of leaks and if you catch them can snap off.
Likewise all the auto air vents with the exception of the one on heat store are now manual rad key type.
We have modified all the Grant combi's we look after.

 

[markio123]

Exedon thank you.

So I need to drain down the boiler, drain plug behind burner.
Remove the pressure switch, fit 1/4" BSP plug in its place, fit link wire where the sensor was wired into the main board
Remove the auto air vent NOT the one on the store and replace with 3/8" radiator drain bleed valve.
Possibly replace the AAV on the store as it would make sense whilst I've got the boiler drained?

Thanks.

 

[Exedon]

There is a valve on return the one that's blue one turn that off we normally turn off both pump valves on heating pump .
You will then only have to drop pressure in boiler to work on it Just open drain off near Burnet to drop pressure.
No full drain down required.
Be very careful removing the vents that are brazed onto the copper pipework easy to distort.
Get a spanner on brazed socket first.
Plus be very careful venting heating pump we have had several customers blow the board by getting water on it.

 

[markio123]

So Friday evening last week after pressurising the boiler to 1 bar, during the night one of the breakers on my DB tripped out and would not reset. I went and checked the boiler , zero pressure and a whole lot of water in the bottom of the boiler and a damp jacket. Turns out the pressure switch that was leaking decided to leak properly.

As you guys probably know the plastic degrades with the heat and you are left with no way of removing the sensor easily as it just snaps off and you are left with the remnants of the sensor. I ended up drilling and tapping the hole and then suctioning the area below with a silicon pipe adapted to plug into my vax.

I have now capped off where the sensor was and linked out the board.
Removed one of the AAV's and replaced with a radiator bleed valve
Put a new AAV on the hot water store.

Pressure is now consistent at 1 bar after a couple of days.

However I still have my original issue.

Hot water works perfectly.
Central heating works perfectly as long as the hot water is switched off. If the hot water is switched on the central heating pumps cycles ON and OFF at varying frequencies and the rads never get hot at the bottom. When the CH pump is switched off the DHW pump is active as per my picture at the start of this thread. If the central heating is turned off, the DHW and reheating of the heat store seems to work as it should do, ie not consistently cycling.

So if I look at what inputs to the PCB are driving this behaviour, then it must be either heat store or flow thermistor, both of which have been changed as well as the PCB.

Any ideas please. thank you in advance, I appreciate it.

 

[markio123]

So I've spoken to Grant technical. After describing what is happening they have suggested it is most likely the non return valve on the central heating pump that is causing the issue. I know the symptom should be some heat on the ch pump outlet pipe when no heating is being called for, I must say I haven't noticed that but i'll check. Looks like a relatively easy swap if required.

 

[snb1]

So I've spoken to Grant technical. After describing what is happening they have suggested it is most likely the non return valve on the central heating pump that is causing the issue. I know the symptom should be some heat on the ch pump outlet pipe when no heating is being called for, I must say I haven't noticed that but i'll check. Looks like a relatively easy swap if required.

it could be tha, but you don,t get heat leaking out past it. It draws cold water from heating back down it and cools the exchanger. Easy test is to turn the pump isolater off and see if it stops the hot water from trying to reheat

 

[markio123]

it could be tha, but you don,t get heat leaking out past it. It draws cold water from heating back down it and cools the exchanger. Easy test is to turn the pump isolater off and see if it stops the hot water from trying to reheat

Well he was kind out of ideas and that's all he could suggest.
So I'm trying to understand what you say is an easy test,
isolate the pump (I'm thinking on outlet side?)
turn the hot water on with no central heating?
What is supposed to happen if the non return is faulty?
I probably got that wrong, but if you could explain a little more it would be appreciated. Thanks.