Another seasonal heating question

[the snooper]

after reading what type of boiler it is i agree with woz the diaphragm doesnt control gas (they did on powerless multipoints) flow but what is does do is control the diverter valve which diverts the main central heating flow through the heat exchanger which in turn heats up the domestic hot water supply

 

[Wozzaaah]

That diaphragm being faulty still wouldn't slow down the flow rate though snooper, the micro switch it actuates can only be on or off so on = hot water, off = cold water.

Alex, do the other hot taps flow ok or are they all slow?
Recently, the tap on our basin flowed well when first turned on but as the water heated up it slowed to a trickle, so much so that there was insufficient flow and the boiler would cut out.
Took the tap apart, cleaned a bit of crud out and it now flows like a good'un.
If it's JUST the bath tap then this should be the first port of call if you haven't already checked it.

Seems queer it can heat radiators but not water?

This is my understanding of how a combi works (it may well be wrong and if so then I'm more than happy to be corrected ).
The CH side is a closed loop, the water is heated and pumped around the loop, back to the boiler, reheated etc.
When you turn a hot tap on, a flow switch tells the boiler to change from CH to DHW. The diverter valve closes the CH loop and diverts the water that's currently in the boiler through the plate heat exchanger so the small amount of CH water inside the boiler then heats the water that is now flowing through the plate heat exchanger.
If there's any restriction anywhere in the system then the flow of water is lessened.

 

[the snooper]

alex has said the water flow rate is ok its just the fact that it doesnt heat up enough although it does get warmer if you slow it down

here is a litte more

The diverter valve performs a critical function within the overall operation of the boiler, being activated every time there is a demand for domestic hot water. One of the main advantages of these combination boilers is that they provide domestic hot water at mains pressure, eliminating the need for cold water tanks and shower booster pumps. The diverter valve is the component within the boiler that responds when a hot water tap is opened and diverts primary (heating) water to the main bi-thermal heat exchanger in which the mains pressure domestic water is heated to a comfortable level.

The valve comprises a brass body with five water connections. On the diaphragm chamber, identified by the eight screws clamping the two parts together. Domestic water inlet/outlet connections are ½\" externally threaded. The inlet, which includes a filter to prevent contamination by dirt, is connected to the incoming mains cold water supply. The outlet is connected to the main bi-thermal heat exchanger, and features an adjustable flow regulator.

The shaft or spindle projects from the centre of the diaphragm chamber and is fitted with black plastic pusher disc that presses on the microswitches when the valve is actuated. Inside this chamber there is the flexible rubber diaphragm, mounted on stainless steel discs, retained in the correct position by carefully selected springs. The diaphragm is made from ethylene propylene WRAS (Water Research Advisory Service) or WRC (Water Research Council) approved rubber, specifically selected to comply with the UK water regulations. The stainless steel shaft is located in PTFE bearings that contain rubber O-rings that ensure no leakage.

The primary body of the valve includes a ¾” primary water inlet connection and two primary (heating) water outlet connections. In the winter, the heating water flows through the 1” externally threaded outlet connection when the valve is in the non-actuated position, and this heating water is discharged into the central heating system and circulated around the heating system before it returns to the boiler, where it re-enters the main heat exchanger. When there is a demand for domestic hot water, the cold mains water entering and leaving the diaphragm chamber causes the valve to change position. Now the heating water flows through the ¾” externally threaded primary water outlet connection to be passed to the main bi-thermal heat exchanger. In the summer, there is no flow of primary water until the boiler detects a requirement for domestic hot water.

so it would seem that the micro switch operated by the diaphragm is purley for summer months when the central heating is not in operation.
its purpose must be to fire the boiler when there is a demand for domestic hot water (summer only

 

[Wozzaaah]

I see no mention of flow rate or of the water getting hotter if he turns the tap down, just that it takes him 30 mins to fill his bath.
Maybe that's what he told you via PM?

Ah, you've added.

No, the diaphragm operates the switch when the CH is called for or when the DHW is called for.
We had an issue with ours last year where the pin wouldn't actuate the swich if just DHW was called for, it would extend but not far enough. The only way we could get DHW was to turn the CH on so the pin would actuate the switch. With the boiler already fired up it would happily supply DHW when the tap was turned on.
A new diaphragm didn't solve it but a new heat exchanger did, apparently ours was scaled up on the CH side with 'magnetite' (black metallic scale) which was restricting the flow enough for it not to operate the diaphragm.

 

[Tigman]

Have you put in a magna-clean on the heating side ,highly reccommended , collects all the black crap in the heating circuit and you can clean them out !

 

[Wozzaaah]

Yes, we had one fitted at the same time as the HE. Cleaned it the other day, it wasn't too bad but there was still a significant build-up on it.

 

[Tigman]

there a standard fit now specially if you put a new boiler on an old system , power flush , then fit the magna clean , saves the new boiler !

 

[BIGMIKE]

First thing first has it always been like this or just happened? Most small combis have a slow flow rate to get the water hot(so the water stays in the boiler longer and picks up more heat) As already mentioned the temp outside will make things worse as its designed to raise cold temp by so many degrees so if cold water is 10degrees colder now than summer its got that to make up straight away.
The boiler basically works flat out for hot water as you need it now, were as heating it slowly heats your rads.
LS80 aren't the best boiler out there but they are quite basic(but can occasionally cause people lots of problems to fix!) Few easy checks, is check hot water with central heating off if the boiler fires up then diaphragm in the diverter should be ok. Iam not 100% if the LS80 has the early giannioni diverter valve with a micro switch on the end, which you can see the spindle come out or if they have the later enclosed type with a micro switch in the middle of the valve?(i'd have to see it)
If the boiler fires up on HW on its own next thing is undo 2 screws on top at the back of the boiler and easiest thing is to remove all 4 screws on the bottom panel then you can remove the outer case(usually have to stretch case outwards slightly). Next run hot tap and look at flame through sight glass and check if goes between high and low flame as you turn HW stat up and down. (This will prove if your HW thermistor is working)
If when your running hot water the flame keeps going high,low,off,high,low,off (hot water will then go cold hot,cold,hot,cold)then left with faulty primary thermistor(quite common and cheap fix) or restricted plate heat exchanger or restricted main heat exchanger. Generally not scale but black sludge. This will also usually cause a kettling noise before flame goes off and back on again. if this is the case then heat exchangers can be sonic cleaned rather than replaced.
Any more info you need just ask
Mike

 

[Wozzaaah]

Cheers Mike, welcome to the forum.
Alex hasn't really described his problem too clearly but from what I now know, his problem is that the flow is good but the water just isn't getting hot enough.

 

[BIGMIKE]

Thanks only just bought the mig welder and stumbled across the forum but found loads of useful information on here so thought i'd try and help with something i know about as iam sure i'll have loads of mig questions!
Like i said first thing first is has it always been like that or just started because loads of combi's out there take ages to run baths.
Mike

 

[Alex.]

Sorry for poor description. The HW taps in kitchen and bathroom flow with good pressure, but to get any heat I have to turn them down to a trickle. The boiler comes on when HW is asked for and stays on as long as the water runs.

The boiler has never been brilliant at heating water, this is my first and last place with one! In other places I've had separate boiler, HW tank (with immersion heater) and they just worked!

Rant over.

Alex.

 

[the snooper]

bike mike came up with a simple test
run the hot water for a while stand next to the boiler then have someone turn off the hot tap and listen if the boiler makes a noise like a kettle if it does he says the heat exchanger could be blocked

see his post

 

[Pete.]

GAs engineer cleaned out our heat exchanger about 10 mths ago by filling it with vinegar, giving it a good shake about and re-fitting it. Made a good bit of difference. Now we just had them out again and they want to sell us a magna-clean filter, which comes with a new heat exchanger for £250. I'm thinking of just getting the magnaclean and fitting it myself and flushing out the current exchanger the way the fitter did.

 

[the snooper]

if the vinegar worked i assume it was white vinegar i would leave it in overnight

 

[BIGMIKE]

Pete £250 for new heat exchanger and magna clean seems quite cheap for all parts and labour. Heat exchangers can be anything upto £500 for the part depending which one it is. As for cleaning them the only way ive seen that actually works properly is putting them in a sonic clean machine. Was it a large "gas company from britain" who quoted the £250 because thats normally the price for a magna clean on its own(combi system). Then they usually do a sonic clean as part of the job if the blocked heat exchanger is the main problem. They only usually replace if its leaking our that patch doesn't have a sonic cleaner.

Alex as for combi boilers same as anything you get what you pay for. Unfortunately yours isn't a great boiler to start with so flow rate/temperature rise will never have been brilliant and they are prone to sludging up(although this is more due to the water condition in the system). Plus there not the most reliable boiler. There are some big combi's out there with excellent flow rates/temperature rises that are reliable, but they obviously cost more!

 

[Wozzaaah]

When ours went wrong we had a new diaphragm in the diverter valve which didn't cure the fault so we then had a new heat exchanger and a magnaclean fitted, £376 all in including the diaphragm visit.
It's playing up again at the mo but rather than hijack this thread I'll start another (don't run away Mike ).
I asked about cleaning the heat exchanger but the engineer said it's simply not worth doing on one that was as cheap to replace as ours as the boiler's out of action and when the cost of labour's factored in it's not much more expensive to replace it and cleaning it might not work anyway.