Boiler DHW keeps going cold

rob7475

booksandbikes said:

- The boiler was installed in 2020, so fairly new (or at least, not old!). It is still under warranty, so hopefully a heat exchanger replacement will be covered 🤞

- pretty sure there is a filter attached, from the images I have googled. Will make sure it is checked

- the problem still happens whether the heating is on or off. I have tried various combinations, and it still cycles hot/cold

- I've turned the boiler temp down to 45C, and it didn't cycle just now, but I will try to repeat it again to see if the same thing happens

I have booked it for a a service later this month - I will report back with what the issue was. 😊

If turning the hot water flow temp down stops the cycling, it's almost certainly a plate heat exchanger issue. As long as you've had the boiler serviced annualy, it should be covered under warranty - give the manufacturer a call and they'll arrange a visit.

booksandbikes

WIAWSNB said:

Do you recall what type of system cleanse was carried out on install?
How old is the original system - rads and pipes?
Pic of the filter? That is usually a DIYable task to check, but fully understand why you might not want to.
I'd ask to see the filter contents - if there is notable sludge, it'll suggest the system wasn't cleaned thoroughly, and is likely behind the P2P failure ( assuming that is the problem). So, a repair should be covered.

This is what was on last years service invoice: "Annual service on boiler. Remove and clean magnetic filter. Remove and clean condense trap. Check flue. Check pressure, check operation of heating and hot water". So not sure what type of cleanse.

I know some of the radiators were installed in 2020 along with the boiler, but cannot see if all the pipework was replaced. 

This is a pic of what I assume is the filter??

booksandbikes

Eldi_Dos said:

@booksandbikes

How long does this hot and cold cycle last for, is it just a few seconds or several minutes?
If it is only seconds could the initial run of water have been sitting in pipework and have came up to ambient temperature followed by cold water coming in from the main causing the variation in temperatures until the boiler stabilise's.

It usually lasts for several minutes, but strangely it hasn't happened in the last few days. When it cycles, it usually does it a number of times and I can see that when the temperature drops the flame icon on the display disappears, as presumably the boiler isn't firing. Then it can take around half a minute before it fires up again and the temperature starts going up.

WIAWSNB

booksandbikes said:

WIAWSNB said:

Do you recall what type of system cleanse was carried out on install?
How old is the original system - rads and pipes?
Pic of the filter? That is usually a DIYable task to check, but fully understand why you might not want to.
I'd ask to see the filter contents - if there is notable sludge, it'll suggest the system wasn't cleaned thoroughly, and is likely behind the P2P failure ( assuming that is the problem). So, a repair should be covered.

This is what was on last years service invoice: "Annual service on boiler. Remove and clean magnetic filter. Remove and clean condense trap. Check flue. Check pressure, check operation of heating and hot water". So not sure what type of cleanse.

I know some of the radiators were installed in 2020 along with the boiler, but cannot see if all the pipework was replaced. 

This is a pic of what I assume is the filter??

Yes, that is the magnetic filter. It has the lid removal wrench sitting in place on it.
It's a householder task to check - if they want to. But your service fellow clearly includes this, which is good.
He hasn't mentioned, tho', what he actually found inside it - that's the important bit. It's a good indication of system condition.
If it's nigh-on clean, then great. But if it has a significant coating of black sludge, that indicates the system wasn't thoroughly cleaned at the time the new boiler was installed (or, less likely, the rads are continuing to corrode...).
Next service, I'd ask to see what's been collected.
By 'system cleanse', I'm actually referring to what was carried out when the new boiler was installed - how thorough this was.
'Old' CH systems will almost certainly have some sludge in them, usually sitting in the bottoms of rads, and coating pipes, especially those at low level. This sludge is anathema to modern combi boilers, as the water channels in the P2P are very narrow. 
Bottom line - if there is visible sludge, then you have cause to be aggrieved. And, yes, it should be covered - either under the boiler's warranty, or because the system wasn't cleansed to the required BS. 

qsk

I have the same boiler and similar problem.  In my case, I have temperature set at about 45 (washing up). The water run hot for some time and then turn cold. The flame is on but the boiler doesn't sound like running. After about 1 min, you can hear the boiler start working again.  Hot water comes back and persists. I usually do not run heating the same time as I use hot water from boiler (I have a hot water cylinder for shower etc). I don't see similar problem with heating. Does this indicate any problems with heat exchange or diverter? My warranty runs out in a few months.

WIAWSNB

qsk said:

I have the same boiler and similar problem.  In my case, I have temperature set at about 45 (washing up). The water run hot for some time and then turn cold. The flame is on but the boiler doesn't sound like running. After about 1 min, you can hear the boiler start working again.  Hot water comes back and persists. I usually do not run heating the same time as I use hot water from boiler (I have a hot water cylinder for shower etc). I don't see similar problem with heating. Does this indicate any problems with heat exchange or diverter? My warranty runs out in a few months.

What type of boiler? You've suggested it's both a combi and conventional. . 

marcia_

 I need s new boiler. The engineer ordered the diverter and came to fit it today. He can not remove the old one without breaking, its plastic and it wont budge which will then leave us without heating in addition to no hot water for 2 weeks so far

qsk

WIAWSNB said:

qsk said:

I have the same boiler and similar problem.  In my case, I have temperature set at about 45 (washing up). The water run hot for some time and then turn cold. The flame is on but the boiler doesn't sound like running. After about 1 min, you can hear the boiler start working again.  Hot water comes back and persists. I usually do not run heating the same time as I use hot water from boiler (I have a hot water cylinder for shower etc). I don't see similar problem with heating. Does this indicate any problems with heat exchange or diverter? My warranty runs out in a few months.

What type of boiler? You've suggested it's both a combi and conventional. . 

It's a combi but wired to heat cylinder as well (Y-plan or S-plan? I can't remember)

WIAWSNB

qsk said:

WIAWSNB said:

qsk said:

I have the same boiler and similar problem.  In my case, I have temperature set at about 45 (washing up). The water run hot for some time and then turn cold. The flame is on but the boiler doesn't sound like running. After about 1 min, you can hear the boiler start working again.  Hot water comes back and persists. I usually do not run heating the same time as I use hot water from boiler (I have a hot water cylinder for shower etc). I don't see similar problem with heating. Does this indicate any problems with heat exchange or diverter? My warranty runs out in a few months.

What type of boiler? You've suggested it's both a combi and conventional. . 

It's a combi but wired to heat cylinder as well (Y-plan or S-plan? I can't remember)

Ah, I see. Interesting!
(It's Y if it uses a single 3-port diverter valve, and S if is has two 2-port valves, which is better.)
I can't suggest anything other than was suggested before - combi hot going cold after a period of running usually suggests a partially-blocked P2P, or a sticking internal diverter valve. 
The only way I can suggest a test is to wait until the CH is cool, and then run the combi DHW. Feel the CH Flow pipe, and see if it also becomes hot as it exits the boiler. This is, however, unlikely to work on your setup since the Flow has an external valve on it restricting flow. So you'd need to shut off the CH flow control on the boiler, and manually open the external valve. Then run your DHW.
Really no idea if the outcome will be indicative.
I'd be tempted to call out the service fellow for the current symptom, and even if they cannot find an issue or cause right now, you will have effectively declared that the issue 'began' before the warranty expired, should it become worse.