Britony Combi SE 100 boiler fault

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)

I'm almost sure there is a gauze type filter in the heating return accessed from underneath the boiler. You must start by checking that as your symptoms point towards restricted circulation.

Its likely to be the blocked return filter.

I thought the filter was accessed from the underneath in the isolation valve but recently went to a late model and it was in the horizontal part of the return.

It could be that they moved it or my my memory!

Tony

Dear Agile and 45yearsagasman, Thank you both very much for your helpful replies. I'll check it tomorrow and let you know. Best regards, Ian

P.S. My Maintenance & Service Guide (Ref 11/2000) says it is in the CH return between the tail and the tap. Edition 4/95 on the Internet says it is 'in the right hydraulic assembly', which appears to be the return pipe from the pump to the main heat exchanger.

I dont know what those words mean but certainly my my memory thinks there are two different places!

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

I am surprised that you did not find a filter!

The diverter valve I thought was a stepper motor? I have not needed to do much on them so I dont know much about them but the mention of a diaphragm surprises me. But I do know that they can be the cause of faulty operation.

Tony

try changing the heating and hot water thermistors we have these go alot .Change both .easy job as well and no real expense.Also fault on these are the clappet valve which the 3 way sits on top of,if you are struggling to get any parts i have many parts for these just let me know thanks pete

Thanks Pete, especially for the offer of parts. 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? What do you mean by the 'Clappet Valve', please? On mine, the 3-Way Valve sits directly ontop of the CH Return Isolating Valve. To the left of that, and part of the same component, is the 'DHW Command' which sits directly ontop of the 'Water Service Tap' (ie the cold water feed). Here's a full update on my day's efforts:

Today 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 does stay very hot to the touch long after hot water tap has been closed but I think that is because it is a large piece of metal that will retain lots of heat for a long time (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, the braided pipe that connects the main heat exchanger flow pipe to the pump, which is the Automatic Bypass, does sometimes feel hot to touch, but not always. We inspected the spring and plastic valve 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, 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? Regards, Ian.

Morning! 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

hi where abouts are u i can let u have pump ,pcb ,3 way clappet new thermisters and any other parts near enough all to rebuild boiler

The measurements on the sensors is not right but I think its your measurement process rather that any fault with htem.

I dont know the exact value for that boiler but usually they are about 13k at 20 C falling to 3k at about 75 C ( which you measured ).

Did you not find the return filter?

Maybe someone removed it?

Tony

Tony, thanks for sensor resistances. I think their OK, tho'. I think someone must have removed the filter on the CH Return Isolating Valve - I'll get a new one.

Peter, thanks for the offer. I'm near Salisbury at the moment but this coming Monday, I'll be returning to Plymouth, where the boiler is. I would be grateful for some parts. Can we get in direct contact to arrange it? I'll send you a personal message through this website with my contact details - OK?

Anyone,

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, 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 CH is on, 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

Peter, it won't let me send you a message unless we are 'friends'. Please could you drop me an email to [email protected]. Many thanks, Ian

Haven't read all the postings but I suggest you turn off the boiler, run the hot tap until the plate heat ex. is completely cold.

Shut off hot tap and run heating...if the plate heats up (other that natural conduction from the flow tapping) then the diverter is letting by.

Did you remove the diverter cartridge and check the parts are free to move/washers supple/seatings clean?