Pulsacoil III - Hot water for only 4 minutes

Hot Water Problem...

Apologies in advance for the lengthy post, but want to give as much info as possible so that someone with the right experience can give me some pointers.

Hot water available only for 3-4 minutes for showering, then it’s cold until next Economy10 cycle.
Problem started only about 3 weeks ago
Water does get hot, up to the usual temperature, but only delivered in limited quantities.

Checked the tap water after shower goes cold = tap water cold too.

“Boiler” used to make a pretty loud rumbling noise when it was charging – that stopped coincidentally with the lack of hot water


So, the checks and observations...

Pipes around the tank hot

Heat exchange plate hot

Pump body – warm-to-hot
Pump seems to be permanently running.
The pump setting (L-M-H) makes no difference.
Pipes on both sides of pump are hot


Top tank water level OK (full), way beyond its minimum line.

Mains power supply OK
Element(s) both seem ok with impedance meter at ~20 ohms

Economy10 switching is OK (well, the storage heaters charge ok)

Diagnostic LEDs....
Water level on (=ok)
Overheat off (=ok)
Overheat button, not popped out (=ok)

Control board  - Red LED - 2 quick flashes every second
(looking up into the body of the unit)

Hot Water temp at taps - 55C (=OK) but only a shower's-worth
Shower time till cold = 5 mins max.


Please can anyone with any thoughts drop a reply.

Is there any other information that i can easily check?

Thanks in advance

Andrew

Put a supply onto the heaters & confirm working.
When problem happens is the unit HOT?
If not check heaters and controls.

If the unit is hot
Then check DHW pump
DHW temp sensor
Mixer valve
Plate heat exchanger

May be worth checking that unit takes water from the top tank.

Mike
MGC/H2O

mike wrote:Put a supply onto the heaters & confirm working.
When problem happens is the unit HOT?
If not check heaters and controls.

If the unit is hot
Then check DHW pump
DHW temp sensor
Mixer valve
Plate heat exchanger

May be worth checking that unit takes water from the top tank.

Mike
MGC/H2O

Mike - thanks for the thoughts.

Yes, both heater elements are functional (top and bottom)
and yes, it takes water from the top tank and there's no "low water" alarm showing at any time.
Top tank is about 75% max, so well above its min.

The unit gets hot after a charge
- all the pipework/plate/pump are all piping hot

About 4 mins of hot water is available, then the water goes cold.

In the "cold water" state the pipework/plate/pump are all cold - well, I can safely touch/grab them.

The main pump seems to be whirring - if I listen, I can hear this. If I switch off the electric supply to the pump it all goes silent (obvs).

My thinking...

if it was the pump, then I'd get no hot water to the taps/shower at all??
if it was the temp sensor, then nothing would get hot. Pipes, plate etc would be always cold??
If it was the mixer valve then, in the "cold water state" the main tank and pipes would still be hot??
if it was the heat exchange plate then the pipes/tank would be hot??

Am mighty confused.

Have had two people out to look at it and both gave a different diagnosis.
Both claim to understand the Pulsacoil system.

Chap 1 said "possibly temp sensor"...but he was unsure. Quoted £350 P&L, no guarantees of a fix.

Chap 2 said it's the main heating element, and that he'd charge £800 to drain the tank, fit new element and refill/recommission. But without guarantee of a solution.


Now I don't understand Pulsacoils, but am an electronics eng.

In my mind a temp sensor either works or does not. The fact that the water is perfectly "at temperature" for the start of the process says that the temp sensor can't be duff or the water would be 100% cold. Am I over-simplifying the failure mechanism??

Similarly, if it was the element, then they either work or not - they don't work enough to give a (consistent) 4 minutes of hot water then nowt.

Am mighty confused!! (...as you might be able to tell!)

Can a heating element pack up after just enough charge time to only heat a fraction of the tank of water?? And then work again next charge to the same partial function??

It's a mystery to me... and the wallet is groaning at the prospect of shelling out  £800+VAT for no solution.

Rgds
Andrew

The concept is;

Have you checked the unit takes water from the F & E tank?
If so how?
( Unit might not be full)

You must ensure that the unit is hot.
If it is cold then no DHW.

Try running the DHW and be near the unit.
Place hands on different areas to see what happens.

Mixer valve could be locking up once it gets hot

Pump might be lazy (age)
Even blocked on the impeller
Or again when hot seizing / sticking (remove bleed screw and check etc

Temp sensors etc can go intermittent when in use.

If you want to know how much water is hot in the store after being fully heated. Drain the unit and see how much / how long it is hot.

Also check when running hot water that the header tank water does not rise.
Had that on a BM II. Hard to see but the internal coil had gone on that one.
I would think not your problem as you have a PHE

Another thought, checked the stats in the heaters? They are on max / 75c ?

Also do not spend 800 on it. If that bad replace it.

Very hard with out being in front of the unit. But anyone who knows / work on them should be able to work it out.

You could try Gledhill Response for a fixed price repair. May cover your area.
Will be approx £350:00p and would include 12 months break down cover too.
But check it all out as things change etc.
Mike

Thx Mike,

Update - Plumber had diagnosed the issue as a faulty heating element. I told him I didn't think that was the cause, but, hey, it's his job, right?

So he arrived yesterday with a fresh heating element bought from Gledhill, wrestled to get the old one out, drained the tank, cleared out a load of crud in the tank, fitted the shiny new element, wired it up, refilled the F&E tank and then left without any form of testing, other than it was leak-free.

(You can probably see where this is going....)

So, I'm on Eco10 system, so evening, night and morning charge periods before morning shower....

4 mins warm water and that was it... so ZERO progress with the problem.

Being ready for this, I got my digital thermometer on the case.

BEFORE showering, water temp (at tap) was just 35 degrees. Should ideally be 60+ ??
Shower was chilly after 4-5 mins.
Sink hot tap temp AFTER shower 25 degrees max.
Pipework barely warm to the touch, not hot.

So, pretty much same as before. Now, if anything, a few degrees colder.

What to do???

Not in a Gledhill area, so it's got to be a "local" plumber...and, of course, they obviously say that they know how the system works....

What's the killer question to flush out the plumbers who may not quite be explaining their true knowledge of the Pulsacoil system??

Any pointers greatly appreciated.

Cheers
Andrew

Right
You must ensure that the Thermal store is fully charged / heated.
Take a reading where the store temp sensor is located.

If the DHW pump is running all the time there is a problem. Pump drive PCB may be faulty.
Have you put a volt meter on the pump connections?
The pump will speed up and down to keep the temp stable.

Your mixer valve might be locking out etc more so when DHW has been run and the mixer valve gets hot.

Shower what type? A bar / sausage shower? If so turn water off remove shower. Turn water on and see what happens.

It seems you are ok at the taps but not the shower, correct?

Look at the sensors at the brass end etc. Are the cable stiff ? further along they will be more flexible.

Also as I said before. Heat the unit up. Drain it and see if it is hot till empty. If you have doubt ref the amount.

Also ref any timers make sure they are not dragging etc.
If unsure heat up on over ride if you have it.

And if you were to state your area / location. Someone might be near you who know what they are doing.

Mike
MGC/H2O