Britony Combi SE 100 boiler fault

[Gregorian]

Can anyone advise, please? My britony combi SE 100 boiler, installed in 2001, seems to work correctly EXCEPT that it no longer heats all the rads properly. Are there any common reasons I should look for? The ch flow and the rads closest to the boiler become too hot to touch but those farthest from the boiler can remain cold. Even if I shut those closest to the boiler and carefully balance the rest, the best I can achieve is that they are all fairly hot at the top and cool at the bottom. The dhw works fine. It is in Plymouth where the water is very soft - there is no furring in the house. Over last year, there was a small leak in the boiler which led to the pressure falling from time-to-time and having to be topped up. I have just drained the system, flushed it with fresh water (*) opening only 1 rad at a time to force water through each rad in turn (until the water ran out clear), re-filled it and added fernox Cleaner, run the heating for a couple of days with the rads balanced (as above) to ensure the hot Cleaner reached all parts, then drained it again (plenty more black water came out). Today I'll flush it again with fresh water as (*) above. When the boiler powers up, with the CH knob set to max, the green LEDs light right up to 80 and the flow becomes too hot to touch. After about 10 mins, the flame cuts out as normal. The green LEDs rapidly (in approx 30 - 60 sec) drop to 60 or 50 and the flow becomes lukewarm. After 3 mins, the boiler re-lights and that cycle repeats. I've also noticed that, when the flame is lit, every minute or 2, there is a slight whoosh/revving sound that ends with a sudden bump and the flame simultaneously drops down a little. Then, I think, it goes back up to its original volume. Why is that? It seems to me that, since the flow and the closest rads get too hot to touch, the boiler is heating the water OK and the fault must be to do with circulating it and maintaining it at a sufficient temp. What are the likely causes, please: pump (I've looked inside it and it appears clean and sound); blockage somewhere (I have not yet checked the filters or looked inside the main heat exchanger but I've replaced the secondary one, and I've flushed the system thoroughly); or could it be that the water is being allowed to cool for too long (3 min) or to too low a temp (if so, why?); or could the gas pressure be too low or the gas valve faulty? What are the most likely things I should check/do, please? By the way, i'm an automotive engineer, I've had some previous fixing boilers and a plumber is helping me but I'm not a plumber ... so please be gentle with me!! (e.g. please use layman's language). Best wishes and thanks for any help. Ian (or Greg)

 

[bill577]

new pump would be my first guess as your system sounds like its clean (not that its means anything).

 

[glenno1]

try shutting all radiators but the 1 last on the system.If it heats up ok id guess its the pump

 

[Gary71]

You have a circulation issue of some sort(as you know), normally if it were the pump I would expect you to notice the temp at the hot tap going hot/cold/hot...... But you would need to change the pump to take it out of the equation. The correct operation for boiler on heating is boiler fires on low fire(1/3 of output) on start up for about 90 seconds ish then goes in to high fire(full output), as it gets nearer to boilers set temperature it will drop down to low fire up to the set point, it will then stay off 3-4 minutes to prevent cycling. You will find with circulation problems that the boiler can't clear the heat from the heat exchanger quickly enough when it fires on high so it will just blip the high and drop down very quickly. You can get your plumber to pull off the lead on the high fire solenoid and see if the heating system can handle 1/3 output, it's not a lot of heat so it should take a while for the boiler to get up to temperature.

 

[Gregorian]

Bill, Glenn and Gary, Thank you all for your very helpful replies. I understand your logic and I'll try your suggestions tomorrow and let you know. Is there any way of testing the pump without replacing it (e.g. test its output pressure)? I've also been advised to check if the CH water filter is blocked (there is a gauze filter in the CH water return).
Thanks, Ian

P.S. Gary, you probably already know this but my Maintenance & Servicing Guide shows there are 3 solenoids (2 safety valves and 1 x second stage solenoid) and says 'The safety solenoids open together to allow the gas to the burner. The ignition sequence begins and a continuous high speed spark ignites the gas. ... After about 45 sec the second stage solenoid opens to allow the full gas rate. If a flame is not detected after 8 sec, the security solenoid closes and shuts off the gas.' (The latter does not happen). I understand you mean we should try pulling the lead off the second stage solenoid - correct?

 

[Gary71]

Yep, it won't cure anything but it can give a idea of how much movement you have and stops the boiler pulsing the heat out.

 

[Gregorian]

Thanks again, Gary. Regards, Ian

 

[Gregorian]

Spent half the day on the
boiler. I've dismantled it completely and can't find a filter anywhere!. The
boiler was built in 2001 - maybe they didn't have a filter back then? Also,
there's no blockage anywhere. There is just a thin, black film (from the rads?)
on the inside of every component but water flows through freely. Tested and
inspected the pump with a friend who installs boilers and it is fine. We
concluded the fault must be the 3-way valve remaining permanently in the
position for delivering hot water, even when no hot water tap is open. That
would divert much of the flow from the main heat exchanger through the secondary
one and direct back into the pump/return, thereby reducing the volume and
pressure of hot water being deliverd to the rads. This would also explain why
the secondary heat exchanger remains very hot to the touch at all times (I
presume it should only feel hot when HW is being delivered?) and might explain
why the flame 'blips' ('cos the main heat exchanger is constantly having very
hot water fed back into it via the secondary heat exchanger). I stripped down
the 3-way valve and it looks fine - the diaphram is sound; and the spring &
valve move freely. So, why is it malfunctioning? How is it controlled; is it by
a thermistor? Could it be a faulty thermistor or the main PCB? How can I test
these (the manual doesn't tell me what voltages to look for at what points on
the PCB). Any thoughts, please? Meanwhile, I'll re-read the manuals. Thanks and
best wishes, Ian
​

 

[Gregorian]

P.S. Glenn, thanks for your suggestion. I did try closing all but the last rad and it takes ages to get luke warm - doesn't get really hot at all. As a new pump cost £118 + VAT, I was reluctant to change it on spec. Instead, on the advice of my installer friend, we tested it by removing the large, flat screw the covers the back end of the pump spindle and holding a screwdriver firmly against the rotating spindle. He says, if that stops the pump, it is knackered, but it didn't. It felt very powerful, it rotates freely, ther's no play in the spindle and there's no sign of damage, so we concluded that it was sound.

Gary, thanks for your suggestions too. I did try them. With all 3 solenoids connected, I don't think it ever goes onto full (high) flame. When I disconnected the high fire solenoid I think it did take longer to reach 80 Deg and it did stop blipping. If the 3-ay valve was constantly divertin hot water direct back to the main heat exchanger, that would also make it difficult to clear the heat from the heat exchanger quickly enough, wouldn't it?

 

[Gary71]

It's the mains water pressure and spring on the spindal that controls the position of the , if you look at the position of the micro switch you can see the movement of the spindal, from cold you should feel no heat on the plate heat exchanger during heating mode, if you do you have to looking at the spindal, you can get the spindal etc..... As a kit rather than get a whole assembly also the PCB, thermostat etc have no impact on the movement of the valve.

 

[gaspastemania]

Are you gas safe registered???

 

[glenno1]

you can test thermister by disconnecting the 2 leads and putting a multimeter (set to ohms-resistance) across the teminals then turn the boiler on and if readings fluctuate you can rule this out

 

[Gregorian]

Dear Gaspastmania, My plumber is gas safe registered, yes. I never touch the gas side.

Thanks, Glen. I'll test them again like that.

Does anyone know the voltages and test points that I should test for on the PCB, to test whether the various sensors are working correctly? My Ferroli boiler manual gives them but this one doesn't. Is it possible that the boiler is just not powerful enugh to do a big house like this - 14 rads (but I turn off the 3 nearest ones completely)? Mind you, even with all the upstairs rads turned off, it still doesn't properly heat the 7 rads downstairs. I think I'll take one of the rads outside today and flush it with a hose to see if is is blocked. Thanks, Ian

 

[Gary71]

If the thermister was gone you wouldn't get the flow temperatures you are getting, if the boiler was underrated it would never come out of high fire, you have a boiler that comes on generates heat and goes off because it's reached it's set temperature, the electrical components are doing there job, as a guess you either have a circulation issue or the diverter valve is passing. You could get your plumber to swap around the thermisters to see if that changes anything.

 

[Gregorian]

Thanks, Gary, that sounds very logical. I did try swapping the thermistors over. It didn't make any difference to the CH but, the first time I turned on an HW tap the flame kept going on and off quickly and the water ran hot and cold but I tried it several times after that and it worked fine. I wonder if the initial problem was due to the thermister still being hot after I
took it out of the CH side? Maybe I should just replace them anyway? Here's a full update on my day's efforts yesterday (I thought I had posted it last night but it doesn't appear in the thread):

I had the boiler stripped completely, on her back, with her legs open!! I dismantled every components below the main heat exchanger. I now understand how it all works and am pretty confident there are no physical faults with any of the components. I see how the 3-way valve works and I can see it moving down and depressing the microswitch, when hot water is drawn. As soon as the hot water tap is turned off, it does rise back to the top again, into the CH position. I tested the microswitch with a multimeter and it works correctly. The secondary heat exchanger is cold when the boiler firs starts and only the CH is on but, after HW has been drawn, it gets too hot to touch and stays v hot for a long time. I think that is because it is a large piece of metal that will retain lots of heat (ie it has a high thermal capacity). I did feel the black plastic pipe that enters the pump from the base of the 3-way valve and it was cool when in CH mode. So I no longer think the CH hot water flow from the main heat exchanger is taking a short cut to the pump via the secondary heat exchanger. Also, tthe Automatic Bypass, ie the braided pipe that connects the main heat exchanger flow pipe to the pump, does sometimes feel hot to touch, but not always. We inspected the spring and plastic valve (at tha back of the pump) that shuts off the Automatic Bypass and it looked fine - the spring was quite strong. So I no longer think that the lack of heat to the rads is due to CH flow taking a short cut through there, either. I also think the 2 thermistors (CH and DHW Control) are OK. I measured their resistance cold (about 5000 Ohms) and warm (about 3000 Ohms) - not accurate but about right. I also swapped them over and it made no difference (except the first time I drew HW), so I think they are working correctly. Having done all this, the original fault remains. The only possibilities left, that I can think of are: 1) my efforts to flush the rads has not worked and they need a power flush [possible]; 2) despite our screwdriver test, the pump is not producing enough pressure [less likely but possible]; 3) the spring in the Automatic Bypass is weak and allowing too much of the CH flow to take a short cut [unlikely 'cos the braided pipe doesn't often get hot and my experienced plumber friend thinks there's nothing wrong with the spring and valve]; 4) the 3-way valve is not closing properly in CH mode and is, in fact, allowing some of the CH flow to take a short-cut direct to the pump [very unlikely 'cos it all
looks very sound and clean]. Is there any other possibility? Today, I'll take the end rad off, take it outside and flush it with a hose to see if it IS still bunged up. Otherwise, I'm out of ideas! Thank you all ever so much for reading this, and for the ongoing hel, Best Regards, Ian.

 

[gaspastemania]

Wether or not your plumber is gas safe your only allowed to take cover off boiler if your gas safe registered or a competant person
A, you dont sound gas safe registered
B, you dont sound competant and nor does your plumber .

 

[Gregorian]

Dear Gaspastmania, Thank you for your comment. I hope you won't take offence if I disagree with your statement about our competence. I do fully understand your concern but I have been a degree qualifed Chartered Engineer all my working life, with over 30 yrs experience in automotive engineering and I am certainly competent on anything inside a boiler to do with either hydraulics, mechanics or electronics. My plumber has a lifetime's experience of plumbing and working on boilers. I hope that allays your fears a little. I guess you have plenty of experience yourself on boilers, which I respect, and I would certainly appreciate any advice you can offer on solving this problem, please. I see you are based in Devon. Do you live anywhere near Plymouth by any chance? If so, perhaps you would like to come and help me; or even take over? Best wishes, Ian

 

[diamondgas]

Hi Ian, Just reading through your thread here I hope you don't mind me putting my peneth worth in!

It sounds like you've virtually eliminated the boiler from the equation to be honest. It sounds like all the components are doing as they should. If you had a poorly performing pump, by the way you would have problems with your hot water too! Easiest way to check this is the temp difference between your hot and cold. if you check out the manufacturers instructions it'll tell you flow rate at 35degC. Basically if you've got 35degC or more then your pump's fine!

Okay that aside check out the heating flow and return temps will let you know how quickly the water is circulating through the central heating! Ideally you'd be looking for no greater than 22degC difference. A great deal more than that indicated poor circulation!

What size pipes are supplying your heating system at the moment? Do you know if it's a two pipe or one pipe system? How old is the heating system? How many radiators? Lots of questions I know but reading above my personal thoughts are toward system restriction rather than appliance

 

[Gregorian]

Dear All,

I now think the fault is either an incorrect pump (this has a 15-50 but the Manufacturer tells me a Combi 100 should have a 16-60; and that a 12-rad system needs a Combi 100 with the 16-60) or there is a fault within the boiler with one of the valves in the HW side or the bypass valve.

Does anyone agree or disagree with my reasons for reaching that conclusion, which are as follows? Despite flushing the system pretty thoroughly the old-fashioned way (including taking off the last 2 rads and flushing them with a hose) there isn't any evidence of sludge, only some black water of the consistency of milk rather than yoghurt. Also, the secondary heat exchanger gets too hot to touch within 5 mins of turning on the boiler and stays hot all the time the boiler is heating the CH, even with the cold water feed to the HW side switched off (the manufacturer and one of you guys said it should remain cold unless HW is being drawn - yes? This indicates that primary water is continuously passing through the secondary heat exchanger when it shouldn't, thereby weakening the CH circulation. Finally, the braided steel pipe on the bypass gets hot and cold seemingly at random. The manufacturer says the spring in its valve might have been weakened by overuse and it could therefore be allowing too much primary water to take a shortcut back to the pump instead of going round the CH circuit. Grateful for any views.

Best wishes, Ian

 

[Gregorian]

Diamondgas, Thank you v much for your interest - I'm grateful for any advice anyone can offer! I'll try the temp checks when I go back to the House this coming week. To answer your Q's: the pipes are the standard 15mm copper; it is a 2-pipe system; the boiler was made in 2001 and I guess that was when it and the rads were installed; the rads are the modern sort with cooling vanes sandwiched between 2 heated panels front and back and a grill along the top; most of them have rad thermostats and there is no room stat; there are 14 rads in total but I keep the 3 nearest to the boiler permanently switched off otherwise they get too hot to touch and the downstairs ones only get warm; the boiler is upstairs. It is a large, 2-storey, Victorian terraced house, typical of Plymouth with solid stone walls and high ceilings. Difficult to heat but that doesn't explain why the flow pipe and 3 rads nearest the boiler get too hot to touch and those in the rest of the house feel hot only and the touch, and those farthest away only get luke-warm. Having seen my reasoning above, what do you think, please? Best regards, Ian

 

[diamondgas]

Hi Ian ... hmmmm ... re-read again and your conclusion sounds logical. Thing I'd be doing to check that the diverter was operating correctly is, from cold, hand on the return pipe. If it heats rapidly then it isn't shutting off the domestic circuit! Also checking out how rapidly the flow heats up. Ideally it should be gradual rather than rapid.

Regards pipe sizing You do have at least 22mm coming from the boiler yeh?

Now i know you've said you've checked for a filter, the manu instructions say there's one in the return connection furthest right! It may be incorporated in the valve itself! I've only ever worked on one Chaff of this era by-the-way!

Regards the pump, it looks like a grundfoss. You should be able to change the head for a 15/60 no problem. You can purchase the head on it's own, about £60...

You say the first three rads are turned off. Try the circulation with them turned on see if makes any difference just to rule out or in a blockage beyond these three radiators.

I''m edging towards the diverter valve as most likely problem, dislodged pump impeller maybe then beyond that a restriction elsewhere! Temperatures differences can tell a lot about how the boiler is working! Oh, bye the way! When your feeling the return pipe check the return above the pump into the boiler and the heating return under the boiler. If there's a huge difference between them then the diverter comes more to focus once more! The bi-pass is less likely to effect the circulation that much in my opinion!

 

[Gary71]

Until you deal with the movement of water thru the plate heat exchanger you are just messing, change the diverter valve assembly, it comes as a kit, change the bypass while your at it as it's fairly inexpensive, this advice is based on being the manufactures tech(for my sins)

 

[Gregorian]

Many thanks, Gary. I'll do that but the whole right-side hydraulic assy below (including the 3-way (diverter?) valve body P/N 1302411 and the Water Control valve P/N 1305290) was replaced only 2 months ago. I spoke to Ariston and he saide he had never known a new one to be faulty. Nevertheless, I shall clean and/or replace the valves again. He also said that a Combi SE 100 should have a 15-60 pump but this one only has a 15-50. The parts short list in the maint manual suggests the either boiler can have either pump. I plan to upgrade the pump anyway 'cos it is a large system. Is the volute (air separator assy) common to both pumps so that I can just change the pump itself or must I change the volute/air-separator too? The parts shortlist shows they come together (PN 1303461) but I've been advised that I coukld just change the pump itself.


Many thanks,

Ian

 

[ricky1]

The Combi SE was Chaff's replacement for the most unreliable boiler ever made (Brittony 80) and whilst they did away with the original faults the combi se introduced a whole new load. Chaff then got bought out by Ariston, talk about the blind leading the blind

 

[jtsplumbing]

Hi just been reading about your boiler ! Seems the fault is with the system and not the boiler , old style house ,what is the total output of all the radiators ? what is the location of the boiler ? Check the pipe size on the system , sounds like you have to much 15mm and not enough 22mm, meaning that the heat can-not get from the boiler quick enough, on these old style houses the more 22mm on the system the better. You did-not say what type of valves you have on radiators, if TRVs make sure that they are on the flow side of the system (unless bi- directional type)