DHW Problems

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DHW Problems

Post  Neil C on Tue Jan 24, 2017 12:02 pm

Good evening,
Would appreciate anyones assistance with a problem I am having with my DHW on Boilermate 3.

Background:

Approx 2 months ago, I replaced a radiator in my ensuite bathroom. I isolated all of the individual radiator inlet and outlet valves for the rest of the upstairs rads. After replacing the ensuite rad, I topped up the expansion tank after adding a bottle of system inhibitor fluid. Although I did have some initial problems with removing all of the air, I did manage to successfully maintain the water level in the expansion tank (after initially the level dropping a couple of times). I have had no further problems with the Central heating.

Problem:

I have noticed that over the last few months (probably coincidental with the rad change, but not definitely so) that I have had to increase the temperature of the shower mixer valve to get a hot shower, to the extent now it needs to be on full hot to get an acceptable shower. Hot water to kitchen sink also noticed to be significantly cooler by the wife, so have investigated and can report the following:

F&E tank level above the cold water feed inlet pipe level, but not overflowing to outside.
F&E tank water temperature 39 deg C (warm, but not too hot to not be able to place hand into).
Plate heat exchanger pump free to turn on centre spindle.
With no draw off from hot water system, Heat exchanger and heat exchanger pump feel very hot to touch.
With hot water tap open, pump does not appear to start, yet temperature of plate heat exchanger pump casing drops, as does the temperature of the heat exchanger (goes cold).
I have operated the speed switch on the side of the plate HE pump, and with a screwdriver from the casing to the ear, cannot notice the pump changing speed, but can hear the vibration from the PCB reduce as the speed reduces. (I understand this is reasonably common to hear the PCB buzzing). I do not believe the pump is turning on.
I have observed the the orange/green lights on the PCB and they appear to be coinciding with the demands of the system. the red light no 14 has not been on (solid or flashing) therefore no fault codes indicated.
I have observed all the system in the various demand modes, and do not believe there is any issues except, would expect orange light 13 to flash when hot water tap is opened, and the pump to kick in which it is not.

Questions:

1)Does this all point to the hot water flow switch not operating and therefore the pump not kicking in? With the system switched off, I checked for resistance between red and yellow wires on the flow switch. I had continuity. I then opened the hot water tap (system still de-energised) and thought that the flow switch would go open circuit, it didnt, it stayed closed circuit, which could indicate the switch is jammed in one position?
2) Could it be a problem with the hot water temp sensor?
3) What makes the plate heat exchanger pump start?

Any help gratefully received. Hope the pics make things clearer !





Neil C

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More Info

Post  Neil C on Tue Jan 24, 2017 12:27 pm

Have just been reading more topics on the forum, and wondered wether there could be be a PCB fault? I have 2 PCBs and they do not have the LCD display on either of them as shown in the manual. (please see pic above). I do think that the problem is that the plate HE pump is not getting a signal to switch on when hot water is demanded by a tap/shower.

Any thoughts appreciated.

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Re: DHW Problems

Post  mike on Tue Jan 24, 2017 1:25 pm

Just to let you know.
Not all the parts are available for your unit.

Mike
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Parts

Post  Neil C on Tue Jan 24, 2017 1:46 pm

I'm beginning to realise that Mike looking online for possible replacement parts. Just need to be more sure of the diagnosis before I start changing parts.

Any thoughts from what i have described?

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Re: DHW Problems

Post  mike on Tue Jan 24, 2017 3:01 pm

You turn a hot tap on.
Flow switch detect you want hot water.
DHW sensor & PHE sensor
And the DHW pump all from the PCB

Check page 25 in the manual
Check for fault codes see manual page 26 /27

Voltage at the pump?

Are you say there is a display on the PCB's but they are not light up?

Mike
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Re: DHW Problems

Post  Neil C on Tue Jan 24, 2017 4:04 pm

Mike,

Many thanks for your reply.

This is a 2 PCB, therefore there is no LCD read out on the SAC or DHW speed PCB.

Having now found the correct manual (I was looking at the single PCB manual previously), I can confirm that in accordance with pages 25/26/27, there are no fault codes. This is what is strange to me! No fault codes (unless LED 14 (red) has blown). But I am also showing a full LED count on the Store temperature green LED's 1-10. If I understand correctly, a fault code is indicated by red LED 14 on with a green LED (1-10) to indicate which area is in fault.

The voltage at the PHE pump is 0v when no taps are open and slowly rises to 105V when a tap is open, but does not reach 240v. There is 0V across the red and yellow terminals of the flow switch either with tap open or closed either measuring AC or DC voltage.

Am I right in thinking that as soon as a hot tap is opened, the flow switch should sense the flow of water and open to allow cold water through to the PHE/3 way valve?

When a tap is opened, the store LED's reduce as the temp in the store reduces, but once the tap is closed, does recover temperature in 5-10 minutes. The boiler pump and sensor are kicking in as expected.

The red LED on the upper speed PCB is blinking at approx 1.5 sec intervals (which says to me low frequency therefore indicating system is ok as opposed to high frequency which could indicate a temperature measurement error) - have I got the frequency of flashes correct or have I got them the wrong way round and this is actually my error code?

Your continued help is much appreciated.


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Re: DHW Problems

Post  mike on Tue Jan 24, 2017 4:49 pm

You have the twin board BM III
If you read the book. If the DHW pump runs all the time the flow switch is at fault.
It does state cleaning it.
And the in line Y filter.
I am not 100% sure but I think the flow switches are not available.

I have not got many BM III's in my local area.

I might have looked at 2 or 3 at the most.
Last one I found out not all parts are available. So now I can see no point.

You could try the above.
But in all fairness it may be time to think about upgrading.
Is your boiler old to?

If an average house (not huge) I would consider installing a really good combination boiler.
At the moment my first choice would be;
Baxi EcoBlue Advance. Good guarantee
Worcester Bosh
Or Viessmann Might be spelt wrong.

The bigger the better to get the DHW flow rate.

If not it would be replace the BM III with what ever
Choice of Thermal stores open vented.
Or unvented cylinder
Plus boiler if required.
Again Baxi do a heat only Eco Blue advance. The advance is much better than the Eco blue

Gledhill do a Boilermate BP unit or a stainless steel one.
Both work out the same.
BP comes bare so lot to buy etc and fit.

Stainless comes complete and need to connect.

Albion & range do thermal stores along with many others.

Mike
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Re: DHW Problems

Post  Neil C on Tue Jan 24, 2017 4:59 pm

Mike,

Thanks again for the reply.

i do not think the DHW pump is running (although it is free to turn) which i think is what the problem is as I wonder if it is getting the correct signal to run. 105V seems low and no change in voltage across the flow switch. What voltages should I expect at PHE pump terminals when a hot tap is open? Is the voltage at the flow switch A or DC and do you have any idea what voltage it should be?

thoughts ?

Many thanks.

Changing the boiler and store means approx £5500 (had a quote for a modern similar system within last 6 months) and is not my preferred option at that price! I am in a 4 bed 2 bathroom house. Water pressure is excellent here and do not want to go to a combo boiler

Regards Neil

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Re: DHW Problems

Post  Neil C on Wed Jan 25, 2017 5:41 am

Mike,

Could anything that I have said point towards the PHE or cold feed pipe being blocked/scaled up? It seems to be a common ailment and wondered on your thoughts of whether the symptoms are conducive with a blockage on the DHW part of the circuit?

Regards Neil

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DHW Update

Post  Neil C on Wed Jan 25, 2017 2:32 pm

Update after todays fault finding.

So a friend of mine came round who also has a Boilermate 3 and coincidently has a very similar issue with hot water going cool after a short period of time. i also spoke over the fone to a gas fitter friend of mine, who although not familiar with Boilermates, was able to provide some logic to our reasoning.

We realised that the DHW pump was constantly running. We powered down and started checking the microswitch on the flow switch and noticed that the microswitch was not sitting all the way into its locating position. I checked for continuity across the microswitch and confirmed it was good. Then I opened a hot tap and witnessed the small lever on the flow switch body move up and down as the tap was turned on and off. After refitting the microswitch correctly and powering back on, the DHW did not run this time until a hot tap was opened. So the DHW is now operating on and off via the flow switch correctly rather than constantly running whether there was a tap open or not. That now negates a problem with the flow switch and the pump is operating correctly and is pumping water.

Unfortunately, this has not cured the lack of enough hot water.

So now the situation is that there are still no fault code indications on any PCB, and the CH system and boiler cut in/out and store temperature are still all fine. Only problem remains that after a few minutes of opening a hot tap, the hot water cools right off (not freezing cold, but certainly not hot enough, i.e. shower mixer valve has to be on full hot to get a barely hot enough shower).

With all hot outlets closed, the PHE is hot from top to bottom, DHW pump is off, but casing is hot . As soon as a hot tap is opened, flow switch opens and starts DHW pump. Temperature of PHE quickly cools from the bottom up towards the top of the heat exchanger. Water from cold feed passes through strainer, trough the flow switch and into bottom of the PHE on the right hand side. Comes out of the top of the PHE very hot, past the temp sensor and to the mixing valve. The outlet from the mixing valve to the tap draw off is at a reduced temperature than the water going in from the PHE. I realise that this is the mixer (or anti scalding valve), but wonder if this is the issue as its allowing too much cold fresh feed to be blended with the water from top of the PHE?

So my questions are:

1) Do I have an issue with the mixer valve?

2) Should the PHE go cold all the way from bottom to nearly the top when hot water is being drawn off or does this indicate an issue with the PHE being scaled up?

3) Is there any need to doubt the temp sensor is working correctly?

As I have insurance, Intend to get BG in and hopefully they will follow my fault finding to date and replace one of or all of the 3 parts mentioned. I will also (if they wont) flush the system with Sentinel 400 before adding inhibitor after refilling. If they wont , I'll do it myself!

Interested in confirmation of my fault finding logic and which to change first if insurance wont cough up!

Many thanks






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