Grant MKll hot water problem

[Robert Tyrrell]

I've changed the diverter diaphragm in the valve but the water is still only getting luke warm.
Boiler fires when the tap is switched on but water doesn't get very hot. It does get hot if the heating is on for a while though.
Am I going to have to replace the whole valve?
Don't really want to do that as the connections to the heat x look a bit suspect to me and I wouldn't want to ruin the heat x while replacing the valve.
There's no filter on the system at all and I wondered if the heat x could be blocked at all.

AHA

 

[SimonG]

Checked the ev?

 

[Robert Tyrrell]

Nwditot Must be the result of spending a week in Ireland

 

[Robert Tyrrell]

Update
I've checked the ev and its fine.
I've completely rebuilt the dv as well so that should be ok but still only luke warm water.
Does one of the switches on the dv control water and the other heating or do they both work together?

Just to add to the above:
I can get hot(ish) water when I run it slowly but as soon as the flow increases the temperature of the water drops dramatically

 

[quality]

heat exchanger is dirty I would say

 

[Robert Tyrrell]

heat exchanger is dirty I would say

That's what I was thinking but after removing the DV and having a look it appears to be relatively clean.

As it happens the problem turned out to be nothing to do with the DV that I'd so patiently replaced. It was a broken wire from the boiler to the burner.
I was having a look a the wiring and noticed that if I moved one of the red wires while the burner was running, it would stop.
Replaced the wire, after checking continuity just to be certain, and it all works.
10 lps @ 58°

Showed the guests and reported back to the owner - everybody's happy now

 

[Duker996]

Result :smile5:

I recently replaced a complete DV on a grant combi and also cleaned out the heat x, but still no hot water. A couple of calls to grant and one to my suppliers saw me stripping the new valve down to find it was assembled wrong!

I'm pretty certain it was my supplier at fault, not Grant as the bag the new DV came in was already opened. Lesson learnt, don't accept anything thats been opened!

 

[Duker996]

Double post!

 

[Robert Tyrrell]

I'm back to this one again
The Landlord of the property has now emailed to say that although the HW is working fine, the CH isn't.

Unfortunately with the temperature dropping last week I switched it to heating and hot water and now when I switch the stat on to ask the boiler to heat the rads, the boiler does not fire up.
When I turn the hot tap on the boiler fires and I get hot water.
It’s like the reverse problem we had before.
The stat seems to be working fine and is clicking on and off as it should but no heat!

I replaced the diverter as that was causing a problem, then went back again because it started happening again, only to find a wire loose in the coon block at the top of the boiler. I replaced this and haven't heard anything for a while, until now.
Any ideas as to why might cause this 'New' problem? Surely if it fires for HW then it should also fire for CH?

He's getting charged for this one btw

 

[Robert Tyrrell]

Any thoughts?
I replied to my own post in an attempt to get some answers but it doesn't appear to be showing as a new post so I'm trying again

 

[SimonG]

Sticking relay? Had an external mk3 run ch until hw run then you had to unplug before ch would run again.

 

[Robert Tyrrell]

Sticking relay? Had an external mk3 run ch until hw run then you had to unplug before ch would run again.

Relay? Do you mean the 'Heating Switch', as it's called in the MI?
If you know the part number I'd be grateful

 

[lame plumber]

Mr T, get those fingers googling, or just ring grant and ask for there manuals and brochures, wait a day or so and a big box of goodies will arrive with all you need in future, but look here for now Grant Combi MKII

 

[Robert Tyrrell]

Back to this again -
I've fitted a new heating control switch (The round dial one as advised by Grant technical) and although the boiler will now fire when the heating demand is there, the rads still won't get hot.
As far as I can tell (Because I fitted a new one when this saga started) there's nothing wrong with the diverter, and everything works fine on the HW side but as soon as I switch it to heating, the burner fires and the keeps on heating the system (water jacket, not the rads) until it cuts out after about 5 minutes. The HW is then extremely hot and the burner won't fire for HW until I've had the tap running for a good few minutes to reduce the HW temperature by emptying the primary store.
I'm presuming a pump failure but would like further advice on this as the customer needs it to be working (Holiday let) and I've made 3 calls now, each with a little success but not getting the job done.

 

[Geyser]

Have a look at the check valve on ch return. Stick and get blocked.

 

[Robert Tyrrell]

Have a look at the check valve on ch return. Stick and get blocked.

I replaced the check valve as it was stuck but there's still nothing on the heating circuit.
I've checked the temperature of the pipes around it and from the main HX to the diverter, there's heat but there's nothing after the diverter. The pump is running, and getting very hot , so I'm guessing there's something wrong with the new diveter valve that I installed.
HW works fine. The pin pops out to activate the micro switch, and goes back after so I'm a bit confused really, which is nothing new for me

Has anyone got a diagramme of how the parts of the diaphragm diveter valve are assembled, so that I can check it in the morning?

 

[lame plumber]

has similar on a firebird recently, air in the HW storage tank, causing the overheat stat to kick off, just bleed the air and everything started working ok on heating circuit

 

[Robert Tyrrell]

has similar on a firebird recently, air in the HW storage tank, causing the overheat stat to kick off, just bleed the air and everything started working ok on heating circuit

Cant see it being that really as there's no way to bleed the primary store (That I can see anyway), and there's an AAV on the main water jacket.
I guess I'll have to call Grant again, which is a pain as there's no signal at the property.

 

[Robert Tyrrell]

I was on this job until 10:00pm last night so I thought I'd update this thread with the latest on my woes.

I've swapped out the pipe work on the flow side and added an air vent so that I can bleed the air from the flow at the top of the boiler but still nothing.
All the electrics seem to work fine. The boiler fires when there's a call for
HW and it does the same for the CH but still no heat to the flow pipe.
I swapped out the pump this morning with a Grudfoss one because I did the screwdriver test last night and the pump stopped without any pressure at all.
There's still no heat at the rads so I've been looking at the wiring on the boiler and I think I've spotted an anomaly.
There's a link from the pump live to the burner live and I think that this would be the reason that the burner fires for CH as the RS provides the L to the pump.
After looking at the wiring diagrammed I can see that it shouldn't be there, this suggests that the pump flow switch is being bypassed.
Now my problem is that I can't tell which is the pump flow switch so can anyone tell me where it is on a Combi 70 MKll?

 

[kb76]

Robert did you have any joy on this one?

 

[Robert Tyrrell]

Robert did you have any joy on this one?

Nope- not yet, but I have found out that one of the 'guests' is an out of ticket gas engineer and I think that he's been messing with it as well, which makes things more difficult.
I thought I was going a bit mad because the wiring kept changing and I was certain that I'd left wired correctly

Anyway - Ive gone through a whole pack of fuses trying to isolate the fault and it now appears as though the fused spur is faulty as well because there's still power at the boiler even when the switch is off.
I've disconnected everything and it still blows the fuse, but not every time.
I've re-connected things one by one, and the same happens.
I did get it to fire when I switched it on but the pump wasn't operating so I thought that this might be the primary store heating up first. I got a call for heat from the stat and the pump operated. for some strange reason, I decided to turn the boiler temperature control and then everything tripped out again (It's a brand new temp control, installed correctly btw)
Now they have no HW or CH.
I', going back on Monday with a new burner fan and a new set of controls, just so that I can confirm that there's nothing wrong with the fan.

 

[Robert Tyrrell]

Latest update on this sorry saga.
I've just been to the property and tried to sort the supposed blockage, I thought that it might be the gate valve on the return after removing it I could see that it wasn't.

Last time I was here I linked out the burner so it was running constantly, and it ran until the PRV kicked in, but still no heat at the radiators, well one rad on the landing got slightly warm.

I spoke to Grant technical today and they confirmed that the problem isn't with the boiler but the pipework so now I need to hire a power flushing machine and try again. I really dislike micro ore pipework
There's no obvious place to connect the machine so Dyson think it would be best to remove a rad and fit it between the flow and return?

 

[Robert Tyrrell]

The is an edit to Edit to the previous post

I really dislike microbore pipework

There's no obvious place to connect the machine so d'you think it would be best to remove a rad and fit it between the flow and return?

 

[CWPlumbing]

have you traced the wiring through from both micro switches? I had one where the wire to the pump had been cut! also the wiring was nothing like the wiring in the manual (although logically the same - all the colours were wrong) - had to map it out myself to find the problem