Hot water problem with Chaffoteaux et Maury Sterling PP

[Mr M]

Hello,

I have a Chaffoteaux et Maury Sterling PP combi boiler. The central heating is working as it should but the hot water temperature is not as hot as it should be. When the hot tap is turned on, after a few seconds, hot water starts to come through but then the temperature drops to luke warm, then goes back up again and so this cycle continues.

On checking the boiler when the hot tap is turned on, the burners stay at full height for around 60 seconds and then they drop down for about 6 seconds, then they go back up to full height again for around 60 seconds, then drop down again for 6 seconds. This is continual whilst the hot tap is on and the periods of time between the burners being at full height and at low height is always around 60 seconds and 6 seconds respectively. As a consequence of this when filling a bath, the water is only luke warm.

I have put some sludge remover in the c/h system and am running the central heating when I am not in and will drop this and give the system a flush out at the weekend but I am not sure whether this will actually do any good?

Does anyone have any suggestions as to what the likely cause of the fault is.

Cheers

Mr M

 

[ChrisR]

DOn't know the beast intimately but typically a combi with those symptoms would have some of
1)tap flow rate too high. Keep it down to about 10 litres/minute. Less in winter.
2) Partially blocked secondary (tap water) heat exchanger
3) New diaphragm needed
4) gas rate wrong

 

[Mr M]

DOn't know the beast intimately but typically a combi with those symptoms would have some of
1)tap flow rate too high. Keep it down to about 10 litres/minute. Less in winter.
2) Partially blocked secondary (tap water) heat exchanger
3) New diaphragm needed
4) gas rate wrong

Thanks ChrisR,

1) I did reduce the flow rate from the hot water tap (not sure to what litres/minute though) by slightly turning the ballofix until the flow from the tap reduced but the burner flame does exactly the same and the water temp is also the same
2) If it is this, am I wasting my time with the sludge remover which I have put in? Can the secondary heat exchanger be unblocked by removal and flushing out? or does the boiler need powerflushing or something?
3) I seem to remember from a previous post that there was a way of testing if the diaphragm was passing. Is it that the c/h flow pipe should remain stone cold when the hot water is running and if the flow pipe warms up, then hot water is passing it so it needs replacing?
4) I thought about this but reading the manual it says that "the maximum gas rate for hot water is fixed and is a function of the restrictor size" which suggests to me that it is not adjustable?

 

[Agile]

I dont think the diaphragm is failed if it fires up on DHW demand.

If the rads heat up on DHW the diverter valve is passing but you dont say this happens.

The time constant sounds too long for the secondary HE to be very blocked and I suspect this is a "combination" fault.

Unfortunately this is a quite old boiler and you will find it difficult to find a competent boiler engineer who will be willing to try to find the fault for you.

I suspect you may have to either replace it or put up with it. But it might be a very simple single fault but I doubt it!

The only thing you might try yourself is cleaning the secondary heat exchanger. That might solve it.

Tony

 

[Mr M]

Thanks Tony,

Do I need to remove the secondary heat exchanger to clean it or will the sludge remover which I currently have running through the c/h system do this job for me?

If I need to remove it, is there anything which you would recommend for cleaning it and following removal, what's the process for properly carrying this out?

Mr M

 

[Mr M]

Sorry couldn't answer fully before, I was just dashing out, so.....

I don't think the diaphragm is failed if it fires up on DHW demand.

If the rads heat up on DHW the diverter valve is passing but you don't say this happens.

I left the hot water running for about 10 minutes and the flow pipe (when felt close to the boiler) remains stone cold so it does appear as though the diaphragm is not passing

The time constant sounds too long for the secondary HE to be very blocked and I suspect this is a "combination" fault.

I take it that a "combination" fault is not a plumbing term identifying a boiler part but means more than one fault ???

Unfortunately this is a quite old boiler and you will find it difficult to find a competent boiler engineer who will be willing to try to find the fault for you.

I found a contact number for a local Heating Engineer on the floor by the boiler this morning, so I gave them a ring in the hope that I might speak to one of the Engineers. I got the receptionist or possibly the Engineers wife She said that they had records that they had carried out works on the boiler over the years but nothing recently. She said that they had replaced the diverter valve in November 2004 and the fan in December 2006.

Their labour cost to come out and look at the boiler is £55 exclusive of VAT for the first half hour and £10 exclusive of VAT for every 15 minutes thereafter. Is this reasonable? Any parts required would be extra.

Only very recently I have already spent £200 having a Water Flow Switch and a new timer clock fitted so I am reluctant to get someone out who might charge another £100 in labour before parts. I am not sure what to do for the best

 

[Mr M]

I would really appreciate any responses to the above, as I want to try and get things sorted out over this weekend. Many thanks in advance.

Mr M

 

[superdupergasman]

£170 would get you BG on a fixed price repair. includes labour and parts.

Or you could go on the contract with a repair included for £25 a month.

any further breakdown and you would not get a big bill.

 

[Mr M]

I drained the sludge remover out of the c/h system yesterday and it was pretty dirty. I refilled the system back up and drained it down a couple of times and then filled it up to about 1.2 bar, drained down again but this time turned the filling loop on and flushed the system out whilst maintaining the pressure. Filled it back up and bled the rads. c/h is still working fine but hot water is doing exactly the same thing

Would appreciate any other suggestions or answers to the questions raised in earlier posts. Many thanks as ever for the useful advice

 

[Agile]

The time constant sounds too long for the secondary HE to be very blocked and I suspect this is a "combination" fault.

Unfortunately this is a quite old boiler and you will find it difficult to find a competent boiler engineer who will be willing to try to find the fault for you.

I suspect you may have to either replace it or put up with it. But it might be a very simple single fault but I doubt it!

The only thing you might try yourself is cleaning the secondary heat exchanger. That might solve it.

Tony

It has to be removed and cleaned with a suitable chemical. Search for cleaning plate heat exchangers.

Tony

 

[spacethegas]

prime eg of blocked primary side on dhw calorifier.

sounds like it needs removing descaling/desludging. i would use fx. then a powerflush.

sorry in my experience you have a nightmare boiler. look to replace it.