Pulsacoil A-Class Model PCA145 hot water too hot.

Hello.

I got a call from a customer who has a Pulsacoil A-Class Model PCA145, she had no hot water.
The red light wasn't flashing and no fault codes were showing.
Further investigation revealed that the water level in the header tank was low and the pump was red hot plus had seized (no amount of effort could free the spindle and turn the pump impellor).
I topped up the header tank, replaced and vented the pump, activated the on peak boost (it was the middle of the day) and within 30 minutes she had hot water.
Within a day she called me to say she had no hot water again.
I went back and found that the pump was stuck. I vented it again, freed the spindle and it worked fine. I thought the hot water was a bit too hot but measured the temperature and found it to be slightly less than the factory set 52 degrees C (it was actually 47 degrees C).
She's since called me to say that when she used the hot water after I left it again seemed excessively hot.
That was two days ago.
I've just spoken to her and she says the hot water temperature is now normal.

Having had a look at some of the other threads on this forum I noticed that some people have had problems expelling all the air from the system when the water level has dropped to low and they top it up so I think that accounts for the new pump sticking just after I fitted it. It's working fine now.

With regard to the excessive hot water temperature I suspect that when the off peak timer kicked in (it's set from 12:00 am (on) until 6:00 am (off)) the pump was stuck and the water heated without the benefit of the pump circulating it so it became a bit hotter than normal before the thermostat kicked in and shut down the heating element. The resulting excessive heat build up within the cylinder has taken a bit of time to dissipate due the good insulation properties of the cylinder and to the lady only using the hot water for the bathroom basin and kitchen sink (she only showers and has an independent electric shower unit for that therefore there's not really any bulk use of the water from the cylinder, she did actually state that in the six years she's lived in the property she's never had to extend the timer settings or use the off peak boost) so it's taken a couple of days for her to use the hot water that originally heated when the pump became stuck.

I am a Gas Safe heating engineer whose main speciality is fault finding on combination boilers (I used to work for Vokera) but my experience on Gledhill cylinders is somewhat limited so I'd be very grateful for any advice from more experienced engineers on this subject in case there's anything I've missed.

Many thanks.

James.

You took a reading of the DHW.
But what about the store temperature.
Check for fault codes on the ACB.
You could have a sensor problem.
The ones one the left hand side of the unit bottom two.
If when filling / venting.
It can pay to switch the unit on and the pump will run.
Then off and then on after a while.
This can help with venting.
With an A class it is sometimes worth while connecting a temp supply to the off peak.
Then turn the off peak supply off.
Put the boost on if unit is hot boost will not work!
Then while the boost is on. Apply the off peak supply (temp supply)
The boost should go straight off.
This confirms that the interface relay is working.
Relays can be a problem.
You have on / off peak relays.
The interface one.
And some on the ACB.
Mike

Hello Mike.

Many thanks for the reply, I'll try out your recommendations.

Kind regards.

James.

James-Hackney wrote:Hello.

I got a call from a customer who has a Pulsacoil A-Class Model PCA145, she had no hot water.
The red light wasn't flashing and no fault codes were showing.
Further investigation revealed that the water level in the header tank was low and the pump was red hot plus had seized (no amount of effort could free the spindle and turn the pump impellor).
I topped up the header tank, replaced and vented the pump, activated the on peak boost (it was the middle of the day) and within 30 minutes she had hot water.
Within a day she called me to say she had no hot water again.
I went back and found that the pump was stuck. I vented it again, freed the spindle and it worked fine. I thought the hot water was a bit too hot but measured the temperature and found it to be slightly less than the factory set 52 degrees C (it was actually 47 degrees C).
She's since called me to say that when she used the hot water after I left it again seemed excessively hot.
That was two days ago.
I've just spoken to her and she says the hot water temperature is now normal.

Having had a look at some of the other threads on this forum I noticed that some people have had problems expelling all the air from the system when the water level has dropped to low and they top it up so I think that accounts for the new pump sticking just after I fitted it. It's working fine now.

With regard to the excessive hot water temperature I suspect that when the off peak timer kicked in (it's set from 12:00 am (on) until 6:00 am (off)) the pump was stuck and the water heated without the benefit of the pump circulating it so it became a bit hotter than normal before the thermostat kicked in and shut down the heating element. The resulting excessive heat build up within the cylinder has taken a bit of time to dissipate due the good insulation properties of the cylinder and to the lady only using the hot water for the bathroom basin and kitchen sink (she only showers and has an independent electric shower unit for that therefore there's not really any bulk use of the water from the cylinder, she did actually state that in the six years she's lived in the property she's never had to extend the timer settings or use the off peak boost) so it's taken a couple of days for her to use the hot water that originally heated when the pump became stuck.

I am a Gas Safe heating engineer whose main speciality is fault finding on combination boilers (I used to work for Vokera) but my experience on Gledhill cylinders is somewhat limited so I'd be very grateful for any advice from more experienced engineers on this subject in case there's anything I've missed.

Many thanks.

James.

Hi James
The hot water temperature on any Pulsacoil from model 3 onward is factory set to max 55c. To measure this, you have to run the tap for 1 to 3 minutes before reading the temperature. The first minute of run ,you will get the very hot stagnant water from the exchanger( up to 65c) before the sensor reading received from the pcb will adjust the temperature via the pump speed, to the required 55c. Hope this helps.
kind regards Mario at Mario's Boiler Service

If the airing cupboard has steam in it, the would indicate overheating, the problems could be related to the overheat sensor or even the contact sticking.