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How to Fix Heater Problems

153K views 49 replies 36 participants last post by  Luà s Madama 
#1 · (Edited)
The information here is mainly aimed at Rover 200/400 but much of it also applies to other models.


Rover 25
- Coolant flows from outlet on front of head to heater control valve, then through heater matrix and back to the thermostat where its temperature is used to control the stat opening. When the heater control valve is closed, coolant by-passes the matrix and flows through the rubber block between the pipes directly back to the stat.


MGF Cooling Circuit with Standard Thermostat -




MGFT Cooling Circuit with PRT type Thermostat -
(Diagram by Titanium)






First off – does the heater fan work?

If it does not work on some speeds and this is the problem then refer to this thread. If the heater fan does not work on any of the speeds then the problem is more likely to be a fuse or the fan motor itself. If the heater fan works, but the air is always cold then the coolant has stopped flowing through it, the coolant is cold or the hot air control flaps are not working correctly.

Lack of flow through heater matrix can be due to:

Freezing – thaw out and make sure that coolant is up to strength and changed at regular intervals. Freezing can also cause much more serious damage to the engine and other components.

Heater coolant valve seized / Cable Problems
– the control valve in the heater feed pipe under the bonnet should open and close as the temperature knob is turned. On Rover 200/400 models it is situated near the bulkhead where the heater pipes go through and is operated by a cable from the heater. If it does not move fully, try to work it free with some WD40 or similar. If the knob feels sticky to turn then also read this thread. Or if the knob spins freely it may just be loose on its spindle and need replacing. MGF valve operation is described here, and MGTF heater cable adjustment is here. Another bent control cable thread is here. And another faulty TF valve investigated here.

Typical Heater Valve and Mechanism.



Heater matrix blocked – this can be caused by mayo deposits following a head gasket failure or corrosion debris due to poor system maintenance. Flush through both ways with a hose pipe then run the system with degreaser or descaler in it before refilling with antifreeze mix (coolant). It is often difficult to clean the matrix completely because as soon as a clear path through it exists, the flush will take this route and the remainder will stay blocked. Also, system cleaners will not work where there is no flow at all.



Air lock – perhaps the most common and usually caused by allowing the coolant level to get too low or by incorrect filling from empty. This usually (but not always) results in the engine overheating because it can stop flow through both the heater and the heater by-pass and this will stop coolant from reaching the thermostat in order to open it. System should be topped up with antifreeze mix and if the heater still blows cold the system should be bled to get rid of the air locks. Links to bleeding are –
http://forums.mg-rover.org/showthread.php?t=372901&highlight=
http://forums.mg-rover.org/showthread.php?t=289697&highlight=
MGF only - http://forums.mg-rover.org/showthread.php?t=351375
Note that mayo deposits left in the cooling system, especially if they block vent pipes, can make this process very difficult!

Vapour lock - similar to an air lock, but caused by steam from localised boiling within the engine. The difference here is that when things cool down it will get better by itself as the steam condenses. This is usually caused by a leaking filler cap allowing pressure to escape from the system. The caps are known to be unreliable - buy a new one.

SAAB (Ranco) valve malfunction – late cars had their heater by-pass controlled by a black plastic valve
instead of just a restrictor. This looks like a T piece and is in the heater pipes near the coolant control valve. If this valve falls to pieces, it can block off the heater and allow all the coolant to take a short cut back to the engine. If this happens, the heater may still get hot when the engine is revved up. It may be possible for the valve to be replaced with a 4mm restrictor, but I am not aware of anyone trying this yet. Perhaps it would be easier to replace the entire system with the heater hoses from the earlier car.

Blocked Oil Cooler - High performance versions of the MGTF and 75 have a water fed oil cooler fitted. This forms part of the heater/by-pass circuit and can easily become blocked by mayo following head gasket failure.

Water Pump Impeller Failed - If the water pump impeller has corroded away or become loose the flow may not be sufficient to warm up the heater matrix, but things may improve as the engine speed is raised.


Coolant passing through heater too cold caused by:


Thermostat problem – thermostat failed partly open, thermostat has been removed or someone has drilled a hole through it. Beware! If you find that there appears to be no thermostat fitted, check to see if the vehicle is fitted with a PRT type stat in the pipework. These cars still keep the old thermostat housing, but there is no thermostat inside it, just a carrier for the gasket.
 
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#2 · (Edited)
SAAB (Ranco) Valve

The SAAB valve is situated between the engine and bulkhead in the pipes that provide supply and return to the heater matrix, just before the coolant control valve. The valve is the component in the middle of the second picture with the silver label on it. Earlier systems do not have anything in this area and the link between the two pipes is made inside the block of rubber connecting them at the top of the picture.

When the heater valve is close, water still has to flow back to the thermostat in order to control its opening. This is done by a heater by-pass connection between feed and return pipes. The SAAB valve was introduced in an attempt to increase coolant flow through the heater matrix by closing off the by-pass when not required.

The valve closes off the by-pass when the heater valve is open and then opens fully to allow flow when the heater valve is closed (Cold position). Failure mode seems to be that it sticks open or the washer goes missing increasing flow through by-pass and starving heater. The failed parts can also get into the pipework and cause havoc!

Rimmer Brothers no longer stock the original system with no valve so if you wanted to change back to it the scrap yard might be the only source. Or you could try making up a DIY solution using a 4mm restrictor in place of the valve to act as a by-pass. It might even be possible to eliminate it all together if the original by-pass link inside the rubber block still exists. You would have to check this because I'm not sure if they blanked it off or not. Anyone know for sure?




Original Rover 25 Heater Feed and Return Hose Assembly with no Valve.



Late Type Rover 25 Heater Feed and Return Hose Assembly with SAAB Valve.



SAAB Valve







A couple of diagrams from saabcentral.com -
Labels apply to Saab, but are similar to Rover. (ignore reference to manifold in second diag)


 
#29 ·
The SAAB valve is situated between the engine and bulkhead in the pipes that provide supply and return to the heater matrix, just before the coolant control valve. The valve is the component in the middle of the second picture with the silver label on it. Earlier systems do not have anything in this area and the link between the two pipes is made inside the block of rubber connecting them at the top of the picture.

When the heater valve is close, water still has to flow back to the thermostat in order to control its opening. This is done by a heater by-pass connection between feed and return pipes. The SAAB valve was introduced in an attempt to increase coolant flow through the heater matrix by closing off the by-pass when not required.

The valve closes off the by-pass when the heater valve is open and then opens fully to allow flow when the heater valve is closed (Cold position). Failure mode seems to be that it sticks open or the washer goes missing increasing flow through by-pass and starving heater. The failed parts can also get into the pipework and cause havoc!

Rimmer Brothers no longer stock the original system with no valve so if you wanted to change back to it the scrap yard might be the only source. Or you could try making up a DIY solution using a 4mm restrictor in place of the valve to act as a by-pass. It might even be possible to eliminate it all together if the original by-pass link inside the rubber block still exists. You would have to check this because I'm not sure if they blanked it off or not. Anyone know for sure?




Original Rover 25 Heater Feed and Return Hose Assembly with no Valve.



Late Type Rover 25 Heater Feed and Return Hose Assembly with SAAB Valve.



SAAB Valve







A couple of diagrams from saabcentral.com -
Labels apply to Saab, but are similar to Rover. (ignore reference to manifold in second diag)


i really apologise if i sound stupid, but i seem not to be able to understand what the saab valve actually helps to by pass on the one hand, and what problems could it cause on the other hand..

if osmeone could explain to me, i would be gratefull..
 
#3 ·
I am going to change my pipe work and saab valve tomorrow.

I will have a look at my old valve and try see if I can re jig it to incorporate a 4mm restrictor. If this is successful I will give it to someone on here to try it out on their car for the price of postage :)
 
#4 ·
Hi, I had the problem of no heat so i changed the valve at the bulkhead and had no joy. I also had the problem of the fan only workin on 3 & 4 so I followed your top instructions and got the part from the scrapyard fitted it, all is good. Still had no heat so while the glove box was off I looked under the dash and there is a purple cable that fits on to a push and pull lever which had come off,put it back on and instant heat. Just thought i would post this before you strip your car like i did.
 
#7 ·
Heater problem, R414

Thanks, John, for much useful info on heater.
Mine just blows cold air for past 2 weeks, so will have to get a mechanic to sort it out. I wish I had a workshop in which I could attempt my own repairs. Hope its not head gasket....
Rich.
 
#8 ·
Well, John, have just paid local mechanic £730 for repairs to my R414iS.
Head gasket blown, oil & coolant all mixing, so coolant system completely flushed out. New 3-part head gasket, head machined, 2 valves reground, new water pump, new cambelt, new steel rods. On 75k miles for an 11-year old car. The wife will do her local trips in it for a few more years. We thought it better to spend the cash on it than risk £3k+ on a younger motor with unknown problems.
R has 4 newish tyres, brakes relined 6 months ago, some welding underneath at the same time, and few other signs of wear - apart from the odd rattle!
Rich
 
#23 · (Edited)
Not sure if the rubber block between the pipes still provides a by-pass between them. Any one know for sure?
The heater on our 2004 ZR 160 was never really good. (we only have it for 2 months now) Fixed the oil2water HGF and Fitted a PRRT. The heater went allmost dead. Traced it back to a defect Saab valve. Blocked it off alltogether and it's back to getting warm, and still not being very good ;)

I know that by fitting the PRRT kit on F the heating capacity was less. I figure it will be less on the ZR too.

1995diesel, I've checked the rubber block for you. It still has a bypass in it. 4mm I guess.

I figure I can get the capacity of the heater on the ZR up by closing off the last bypass (in the rubber block). Don't think it will do any harm since the PRRT has it's own big bypass ?

Any suggestions 1955diesel ?
 
#11 ·
Hi guys,

sorry to bring up an old thread but just wanted to say thanks for the info! I've had problems 'bleeding' my coolant for months now... yesterday I replaced my saab valve and all the pipe work around for the old system as above, heater worked straight away! Very happy!! And, the old version was only £2 from a scrap yard, not £68 as the new part is from rimmer bros!

Cheers,
Ian
 
#12 ·
Hi guys, just got my new ZR and the fans are blowing cold. After reading a few threads I'm still not sure of the best way to tackle the problem. I've been on a 100 mile round trip and have done about 500 miles in the last week and there has been no problem with overheating, and no cooling/ oil leaks. Should I start by flushing the cooling system, and if that doesn't work change the thermostat? (as these are both relatively cheap, easy things to do). Other than those things I'm not really sure what to do.

Any advice would be much appreciated!

Cheers, Chris
 
#14 ·
Right so going down from the top..

The fans work fine, and there's no problem with the coolant valve mechanism (the cable and switch are both working fine).

I've bled and flushed the system in effort to get rid of blockages and air locks and the heaters are still blowing cold.

There's no circulation problems and the engine does not overheat, and I'm not loosing any coolant at all. One thing I did notice is that the heater feed pipe (going into the coolant valve) was very hot (after running the engine) but the return hose (leading out of the valve) was luke warm. I don't know if this means there's something wrong with the heater mechanism inside the coolant control valve, not letting water through, or if the Saab valve is related to this in any way??

Any advice would be much appreciated!

Cheers, Chris
 
#15 ·
I can't add anything that I've not already said in the posts above. If there is a big temperature difference across the heater matrix it indicates lack of flow. Could be a blocked matrix or the valve itself blocked. If you have a SAAB valve it may have fallen to pieces. But these points have already been covered.

Best thing to do is to get the hose pipe out and start flushing the system and testing for flow one pipe at a time. Bare in mind that the matrix can be very difficult to clear fully. Often just one small pathway will open up through it.
 
#17 ·
Nice thread! Don't know if this is covered above, but Prestone used to sell a kit to attach to the heater core inlet for flushing. I'd get a similar kit and flush from the outlet side real hard. A hose with 2 clamps might work as well.

Used to use Muriatic Acid for a radiator flush. Makes brass and Al shine. Really caustic so use with caution. Test the solution on a piece of dirty metal if you do that.
 
#18 ·
Rover 25 Heater Probs!

HI Guys, i need some help I have a Rover 25 1.4 2005 model and my friend who is a mechanic has just replaced the head gasket, for some reason the heater has stopped getting warm, he has bled the system 4 times, we have hosed through and cleaned the matrix and replaced the thermastat all to no avail, we are really scratching our heads and need some help! the water pump seems to be working fine too,

any ideas?? thanks in advance
 
#19 ·
HI Guys, i need some help I have a Rover 25 1.4 2005 model and my friend who is a mechanic has just replaced the head gasket, for some reason the heater has stopped getting warm, he has bled the system 4 times, we have hosed through and cleaned the matrix and replaced the thermastat all to no avail, we are really scratching our heads and need some help! the water pump seems to be working fine too,

any ideas?? thanks in advance
read the thread again from the top.
i dont mean to be rude its just every possible situation is listed all nice and in one thread.
Diesel what a thread. ++
thanks for using my pics of the bypass valve
 
#20 ·
Hi Guys, sorry if I am going over something that's already be said however I would like to be 100% sure before I swap out pipes.

I have a 55reg rover 25 which has a T valve which has failed meaning I get no heating. now I still have the old pipes from a rover 200 which had no T valve, therefore can you confirm if would it be ok to just to switch out the pipes and put the rover 200 pipes (which had no T valve) on to my 55 plate rover?

many thanks
 
#21 ·
brian teezer

i have jest changed the head gasket, stat and all the rest. it has a triple layered gasket now but it is overheating. the system pressurizes and doesn't circulate through the rad. when the engine starts heater heats up to normal temp after a bit the stat opens and the heater goes cold. even though the stat is open there is no circulation in the rad. i have tried two stats and no difference and the the pump is good. i have also tried flushing the matrix and rad and they seem fine. ive bleeded the systems 4 times normally and then twice with a vacuum filler so no chance of an air lock. now i have no idea what is wrong :facepalm:
 
#22 ·
Heater problem

Hi there, my heater is not working, have followed info on this thread but still having no joy.

Heater switch works, fan works, have flushed cooling system and used flush cleaner and am getting clean water flowing through. Only thing Ive not been able to do is flush system to lowest point as i cant get the bottom rad hose off cos of those stupid rover hose clips which in this instance is pointing up and I cant get a tool on to it without removing everything else around it!(Grrrr)

Valve opens when heater switch is turned and ive had the hoses around valve off and water flows through ok. Also had water flowing into pipes to matrix and it flows though there too.

Top and bottom rad hoses get hot. Hoses leading to valve get hot but no heat on the other side of the valve (hoses to matrix pipes side) I'm stumped! Can anyone help?
 
#24 ·
knightly 101-from "How to....

"Hi Guys, sorry if I am going over something that's already be said however I would like to be 100% sure before I swap out pipes.

I have a 55reg rover 25 which has a T valve which has failed meaning I get no heating. now I still have the old pipes from a rover 200 which had no T valve, therefore can you confirm if would it be ok to just to switch out the pipes and put the rover 200 pipes (which had no T valve) on to my 55 plate rover?"


Would anyone know if this question was answered?
 
#28 ·
I had this problem on my 05 Rover 25 at the start of the winter and the heater would only work above 30 mph. I changed the SAAB valve / pipe assembly which fixed the problem.

Last night I took the old SAAB valve apart to discover that the valve inside had gone missing causing the water to bypass the heater completely until the engine was running at speed.

I don't know where the valve had gone to as it was not stuck in any of the pipes. One interesting observation was that after changing valve / pipe the radiator fan would cut in more frequently and would run for a few seconds when you turned the engine off which it never did before. This could be down to the coolant flow now been correct or the old valve stuck somewhere in the coolant system.

Andy.
 
#30 · (Edited)
rover 45 1.4 16v dohc. after hgf cooling system modified by fitting prrt(recommended). Used existing top & bottom hoses & purchased another bottom hose & T piece(75 Rimmer Bros).

Ran engine for 1/2hour + with forte cooling system cleaner. Monitored coolant temp, prrt function, cooling fan, etc all worked well. tried to move car about 30ft to be nearer a hose to flush out cooling system. revved engine to about 2500 rpm. loud bang, huge woosh of steam, turned engine of quickly. Bottom hose completely severed. jubilee clip & about 1" of bottom hose complete disappeared. tried to find clip & bit of hose, cannot be found. were pipes knackered(10years old) or faulty- well never know. Water pump is new. Since the origional stat housing is empty. The pump can now shift coolant & generate pressure. This may well have been to much for the rubber pipes. This remains speculation.

2 possibilites for pipe came to mind. (1)the prrt is used in the 75 so used 75
pipes. (2) silicone pipes: the expensive option. I am going to replace all the big pipes with silicon & replace all other rubber pipes. The short pipe between heater control valve to heater is a pain in the arris to get at. yet to sorted.

the prrt is next to air box & above starter motor. T piece by top hose outlet connection. this keeps pipework similar to origional layout.
 
#31 ·
stay away from rovers.....................

never buy a rover 75 k engine
bought a rover 75 on a 2003 plate yeaterday, on driving home heater conked out so couldnt DEMIST WINDOWS WAS DRIVING BLIND.. also termosat went through roof, guy i bought it off showed me receipts from all work done including new head gasket done and all other relevent work to that, i managed to get to garage where i checked coolant and hadsteam and water was pumping out i managed to buy coolant and put it in 1 litre and then at least 4 ,litres of water , i drove a short distance and still car thermsat was to the max, i eventually called a breakdown service, he checked all fuses and they were fine, he then checked engine and said to me i think headgasket is going to go, i said it was just replaced, dosent mater if collant was escaping engine was under pressure, he reckoned engine was ok but to keep and eye on collant, he checked heater inside car and reckoned blower motor gone , but he said to me that all these cars give trouble, i rang guy i bought car from and brought it back to him, what a disaster of a car, i would just say to people stay away from THE ROVER K ENGINE A DISASTER OF AN ENGINE.............
 
#32 ·
hi guys
i no this old thread :)
i have a mg zr 06 platefacelift model 1.4
well my heaters stopped working while ago now just b4 my headgasket went.
had headgasket done aat same time ad new water pump an cam belt.
but since then my heaters just will not get warm
i have tried
flushing the system threw with a rad flush from bottom hose of the radiator.
disconnecting the inlet outlet on my heater matrix flushing threw with hose pipe(flows freely)
checked the heater switch valve opens an closes
replaced the thermo stat
just bought another saab valve but shineing a light threa the t piece end an looking threw other end i can see the light there seems to be a bit of a lip in it but thats it(old 1 was the same)
so put this other 1 on i got and also i cut the rubber block off an reconnected the pipes
as the rubber block got a little bypass in as well(could look straight threw that) is there ment to be anything in that ???

well since ive done all this my heaters get warm when i boot my car but as soon as i slow down they go cold again.

any 1 got any ideas ???
as im out an dont no what to do or wat could be causing this
thanks for your help
 
#36 ·
I know its been a while since anyone commented on this topic but I am having the same problem on a 2004 1.6 Rover 25 after HGF at only 32k. cars now done 36k and heater gets very hot when I put the foot down but stone cold under 2500 RPM.

I have disconnected the temperature switch and wedged the valve open so will only blow hot air still nothing and water flows as it should but I'm stumped.

The only thing I can think of is the heater matrix but that will be expensive.
 
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