Blocked Heat Exchanger?

[Electrophase]

The central heating system (Valliant Ecomax 622, 8 large double radiators) had been losing pressure for several months and I'd been topping it up every other day during the cold periods, but it hardly needed it when the heating was off for a while. The radiators had been making 'tinkling' sounds - maybe some debris was floating around the system, and the boiler (in the loft of a bungalow) had been making droning sounds for quite a while, worse when the boiler shut off and the pump kept running.

The system has obviously been leaking somewhere to cause the pressure drop but there's been no sign of it anywhere. The pipework is under concrete so maybe it was leaking without trace. The guy who services the boiler suggested a leak tracing company, etc, etc, but that was a very last resort as it meant digging up the floors.

Everything was working ok, hot radiators and plenty of hot water. Then a few days ago only the radiators at the start of the system were hot whilst those at the extremities were stone cold. After a few hours the ones at the end of system were slightly warm and it all stayed that way even though the boiler was set to 80deg. The room stat was set at 24 but it never reached that temperature so the boiler was running continuously. Feed to the hot water cylinder (tank stat set to 65) was too hot to touch and the water coming out was hot, but nowhere near as hot as the water going in. I suspected the pump may be faulty and gravity alone was allowing some rads to get hot but not others, so I called in an engineer.

He too diagnosed a pump problem and fitted a new one. That made the situation even worse as there was hardly any heat arriving at the nearest radiators or the hot water cylinder. He partially drained the system, thinking it may be an airlock, but still no good. So he re-fitted the original pump and the system was restored to how it was before he changed the pump.

He now suggests the heat exchanger in the boiler may be blocked and a new boiler is the answer.

Could a blocked heat exchanger reduce the flow enough to stop the radiators at the end of the line from warming up? It sort of makes sense that the heat exchanger has expired given the leak and the 'tinkling' sounds, doesn't it? I'm hesitant to spend new boiler money if that isn't the cause.

 

[EvilDrPorkChop]

Sounds like your 'leak' is probably a failed/unserviced expansion vessel and the water is being pushed out the Discharge. Especially if it's only when your using the heating.

The pump situation, if it was a blocked HEX I would expect the same outcome on either pump. Are you sure he fitted a new and correct pump?

 

[Brambles]

Get somebody out who knows Valliant boilers.

I suspect you have two issues - that outlined above by Dr Pork Chop and :

It is also possibly a partial blockage of magnetite on the return. Not a difficult fix or expensive part.

It is a common problem after 4 or 5 years if you have not got a magnetic filter on the return.

From the symptoms you describe, I am surprised that the boiler is not showing a Fault code. If not F23 will probably appear if there is a restriction on the return.

 

[Electrophase]

DrPorkChop & Brambles,

There's no magnetic filter fitted so, yes, it could be a partial blockage somewhere but all of the rads were replaced within the past 18 months so the system has been drained a couple of times. The expansion vessel was renewed last year and no longer drips outside so that's ok.

The correct pump was fitted as i watched it happening. Because the new pump had a slightly different body he swapped just the head. There has been no fault codes at all.

The real question is, could the heat exchanger have become clogged overnight? One day all was well, the next there was little, if any, circulation.

If I turn off the hot water then the rads eventually reach a reasonable temperature. And if I turn off the heating then the hot water eventually reaches a good temperature. it's like it's all working ok but there isn't enough power in the pump to push it around.

Could it be the power supply to the pump is being reduced in some way by the control board?

 

[EvilDrPorkChop]

The correct pump was fitted as i watched it happening. Because the new pump had a slightly different body he swapped just the head. There has been no fault codes at all.

I think there's your answer, how can it of been the correct pump then? If the new head isn't in the correct rear body it won't work.

Yes there is a setting on the board for changing pump speed, however it had been fine beforehand i'd be looking at the pump.

Regarding your pressure loss, it's more than possible that your HEX is leaking internally and going down the condensate drain. The easiest way to determine this would be isolate the boiler from the system, if the pressure holds it's the system. If it doesn't then it's your boiler.

 

[Electrophase]

I think there's your answer, how can it of been the correct pump then? If the new head isn't in the correct rear body it won't work.

Yes there is a setting on the board for changing pump speed, however it had been fine beforehand i'd be looking at the pump.

Regarding your pressure loss, it's more than possible that your HEX is leaking internally and going down the condensate drain. The easiest way to determine this would be isolate the boiler from the system, if the pressure holds it's the system. If it doesn't then it's your boiler.

Thanks for the advice.

I’m not overly concerned about the ‘leak’ at the moment but mentioned it just in case it was relevant to the main problem - lack of flow.

The original Vaillant (Grundfos) pump is no longer available so he arrived with the updated model. The heads are interchangeable so he assumed it was ok to fit the new head to the old body as it saved a bit of work. Now you mention it, it makes sense that the pump is still the problem and the new head works only with the new body.

I’ll get in touch with the engineer, see how he responds, and then report back!

 

[EvilDrPorkChop]

Thanks for the advice.

I’m not overly concerned about the ‘leak’ at the moment but mentioned it just in case it was relevant to the main problem - lack of flow.

The original Vaillant (Grundfos) pump is no longer available so he arrived with the updated model. The heads are interchangeable so he assumed it was ok to fit the new head to the old body as it saved a bit of work. Now you mention it, it makes sense that the pump is still the problem and the new head works only with the new body.

I’ll get in touch with the engineer, see how he responds, and then report back!

Sounds like your Engineer has just tried to swap it with the new Grunfos UPM3 pump, which I believe won't work.

The original pumps are available - DHS Spares, buy now at dhsspares.co.uk - https://www.dhsspares.co.uk/category/gas-boiler-uk/pumps/brand/vaillant/appliance/vaillant-ecomax-622-2e-2001-2007-vai014

I suggest you get a genuine one, or get Vaillant out for a fixed price repair.

 

[Electrophase]

Sounds like your Engineer has just tried to swap it with the new Grunfos UPM3 pump, which I believe won't work.

The original pumps are available - DHS Spares, buy now at dhsspares.co.uk - https://www.dhsspares.co.uk/category/gas-boiler-uk/pumps/brand/vaillant/appliance/vaillant-ecomax-622-2e-2001-2007-vai014

I suggest you get a genuine one, or get Vaillant out for a fixed price repair.

Thanks for that.

The more I think about it the more I'm convinced it IS a pump problem.

The one in the boiler is VP5/2 ZE and the one he bought with him was VP5/2 S2. The link you sent seems different again so I'll call Vaillant on Monday to ask if the heads are interchangeable.

I'll also ask about about one of their engineers coming out before Christmas - but I'm not sure that will happen now.

Thanks again.

 

[Electrophase]

Thanks for that.

The more I think about it the more I'm convinced it IS a pump problem.

The one in the boiler is VP5/2 ZE and the one he bought with him was VP5/2 S2. The link you sent seems different again so I'll call Vaillant on Monday to ask if the heads are interchangeable.

I'll also ask about about one of their engineers coming out before Christmas - but I'm not sure that will happen now.

Thanks again.

Well, I've checked images of the VP5/2 ZE pump (the one in my boiler) and the VP5/2 S2 (the one the fitter tried) and the impellers are identical. Only difference between the pumps is a higher wattage rating of the S2.

I don't understand why the 'new' pump head didn't pump at all whereas the current one is at least partially working? If the problem is a blockage then wouldn't both pumps perform the same?

Regardless of the pump anomaly I'll assume there's a blockage somewhere and, given the size of debris needed to block a rad valve, I'll assume the engineer was correct and the blockage is in the heat exchanger as that seems more likely. Especially as that may well be the source of the 'leak', too.

I'm awaiting a call from the heating company to see if they can fit a new Vaillant 624/630 before Christmas. I know it's expensive but it will eliminate the boiler from the equation and if it fixes the 'leak' then it will be a lot cheaper than digging up the concrete floors.

 

[Brambles]

Vallaint are generally good boilers - but a number of them - including the 622 are intolerant of operating in dirty systems. It is reasonably common for a restriction of magnetite et al to build up in the return pipe within the boiler feeding the heat exchanger.

From our service records - over the last five years - for Valliant the two most common parts replaced have been ignitor assembly and blocked / perished interconnection pipes.

You have had the pump out, so you will have a good idea of the cleanliness of your system water.

Every case is different - but statistics are often good pointers.

 

[Electrophase]

Vallaint are generally good boilers - but a number of them - including the 622 are intolerant of operating in dirty systems. It is reasonably common for a restriction of magnetite et al to build up in the return pipe within the boiler feeding the heat exchanger.

From our service records - over the last five years - for Valliant the two most common parts replaced have been ignitor assembly and blocked / perished interconnection pipes.

You have had the pump out, so you will have a good idea of the cleanliness of your system water.

Every case is different - but statistics are often good pointers.

That's interesting.

I've been topping up the system, on average, at least twice a week for over a year and all rads have been changed over the past year, too. There was no sludge, visible particles, or even discolouration in the drained water. But the clue may be the 'tinkling' sounds which have been apparent for a while now in some of the rads and, most noticeably, in the hot water cylinder so that may well be where the debris (if that's what the problem is) has come from.

A couple of weeks ago I heard a some clattering inside the boiler which sounded very much like pieces of rust or something circulating inside. There was no sign of damage to the pump impeller but thinking about it, it's quite likely it was coming from the heat exchanger.

I don't suppose 12 months of fresh water being added to the system has done much to prevent crud build-up so changing the boiler is probably a good plan. It's now over 17 years old and has been (mostly) reliable so I've decided on a new Vaillant and a system clean to take care of the hot water cylinder. If the 'leak' persists then I'll have to start looking elsewhere but at least I know the boiler and rads are all ok.

The 622/E is 24kW but having increased the size of most of the rads by at least 25% and adding a 1200mm towel rail, it seems sensible to go for the 30kW boiler.

 

[EvilDrPorkChop]

Tbh i'd keep the EcoMax, one of the best boilers Vaillant ever made.

On your blockage issue, if it's heating your HW cylinder fine and some radiators it won't be a blockage in your heat exchanger.

The easiest way to see, is turn the system on from cold. If the temperature flies up straight away then you've got a blockage. If it steadily rises and the boiler modulate accordingly you've got a circulation issue else where.

Was the pump he brought a new pump or one he had?

 

[Electrophase]

Tbh i'd keep the EcoMax, one of the best boilers Vaillant ever made.

On your blockage issue, if it's heating your HW cylinder fine and some radiators it won't be a blockage in your heat exchanger.

The easiest way to see, is turn the system on from cold. If the temperature flies up straight away then you've got a blockage. If it steadily rises and the boiler modulate accordingly you've got a circulation issue else where.

Was the pump he brought a new pump or one he had?

The water from the boiler is very hot and is still hot when it reaches the radiators and the hot water cylinder. The rads get warm at the inlet side but the return pipes are all cold. Same with the cylinder, the outlet is just warm. The return pipe at the boiler is stone cold on the outside of the casing but gets hotter towards the heat exchanger. That's obviously just heat transfer from the exchanger.

Everything points to poor circulation rather than no circulation, so this morning I drained enough water from the system to reduce the pressure to zero to enable me to compress the flexible tube in the boiler to see if it was blocked. It compressed easily and was pliable, so that's ruled out.

I started the boiler with the pressure still at zero and it made lots of clattering noises. My thinking was that reducing the pressure when it's flowing might allow the blockage to work loose. I then topped up the system and started the boiler. There was more clattering but even after 15mins it was obvious nothing had altered. Incidentally, the clattering noises were definitely coming from the heat exchanger.

I then closed off the TRVs and the lock shields on all radiators apart from two bedrooms and the living room. Given the blockage still hadn't cleared and there's no chance of me getting a new boiler before January, I thought i could at least have heat in the important rooms. The hot water is being taken care of by an immersion heater and backup heat is coming from some electric conversion radiators in the rooms where the rads are closed off.

With regard to the blockage, I'm now certain it's in the heat exchanger. To get the pressure down to zero it meant draining off 3-4 litres of water. That's about how much I've been topping up with every other day or so for over a year. That seems a lot of water to disappear into the concrete without any signs of damp. Hopefully, the leak is in the heat exchanger but I won't know that until the boiler is changed.

The opened rads are quite warm (even hot) and the immersion heater is doing an excellent job. So IF it continues like this then waiting until January won't be too bad.