Vailant boiler no hot water

[evedawn]

We have intermittent hot water. The taps run warm (not hot) for a few secs then ice cold then warm then cold etc. The following have been replaced: sensor, heat exchanger, and a small pipe to the "bladder". Today theplumber is replacing diverted valve. If this doesn't work any other ideas?! ! The boiler is not showing a fault code.

[evedawn]

A big thank you everyone for trying to help

[evedawn]

Boiler eng says it's "modulating too much /long" and then it drops out???? Does this make sense?

[AlBags]

I've taken a long look at diagram ..
Looking more and more like control board fault .. especially as no fault codes displayed in system test mode, and the the other components replaced. What does he think?

[evedawn]

Control board replaced y'day. = £180!

[evedawn]

Boiler eng mystified. He has rung vailant help desk 3 times.

[AlBags]

Yep ..
I was looking at that ..
I think the Aqua Sensor is the problem .. really!
It detects hot water flow, and if it does not .. it just sends cold water through ... More to follow ..

[AlBags]

Cause:
1. When tap opened - Noticed no demand lights (Green & yellow lights both off).
2. Managed to borrow manuals from family friends who have the same boiler/manuals. Checked diagnostics info, i & + = d.22 = 0 when hot tap open (should be 1 to confirm water demand)

Action:
1. On water incoming to boiler (after water service valve) there is an aqua sensor assembly, which was not detecting water flowing through boiler when hot tap is opened, hence no hot water, boiler = demand not present. So the cold mains water passed straight through boiler and out of hot water tap.
2. Isolated power, Closed all service valves, depressurised system.
3. Removed circlip on aqua sensor
4. Removed propeller and cleaned - contained a bit of grit.
5. Removed the breather nut on top of aqua sensor housing, which was blocked - cleaned and blew through it to ensure it was open.
6. Refitted in reverse order.
7. Refilled boiler.
8. Opened service valves
9. Power ON - Opened Hot water tap, green light flashing & yellow on = Hot water!!!!!!


Aqua sensor is in two parts,

The operational principle I understood as follows:

- the reciever (RX) the sensor (fitted on outside of housing and has three wires)
- propellar - the transmitter - as water flows through the housing the propeller spins, and produces an oscillating signal which is picked-up by the RX, the faster the propellor spins the higher the frequency and the greater the demand for hot water.

As the propellor was not spinning before, there was no demand, hence the cold water.

[AlBags]

check the aqua sensor first
press i and + button together to access diagnostic mode then select d.22.Open a hot tap and a display of 1 means it senses water flowing, 0 means it stopped.

Correct input buttons for that boiler?

[evedawn]

Aqua sensor replaced! This is costing stupid money in parts alone. Lucky the labour isn't being charged for (as my hubs co gives this engineer alot of work)

[evedawn]

A/bags that diagnostic code thing may help! Thanks. Plumber now gone but will try tomor.

[AlBags]

I think the sensor must spin .. and it isn't.

http://www.uk-plumbin...045e89fc42597958f0eeb
http://www.bhl.co.uk/...L_194829_AQUA_SENSOR_
http://www.heatingbit...aillant_1_1678_36.htm

[AlBags]

OK.
Same time tomorrow then? : )

[AlBags]

I still think it should be checked for rotation .. It can get stuck by dirt or grit from system. Looks like no filter .. can't be sure.

[evedawn]

Thanks to all of you. You've been so helpful !'yes no doubt I'll be back asking advice tomor:-)

[AlBags]

I'll look back here tomorrow .. if not digging out snow!

[evedawn]

Hi AIbags did that diagnostic ourselves . It shows 1. Do u have a list of what the other diagnostic codes do? No just d22. Thanks muchly for help so far

[evedawn]

Is there any diagnostic to test the heat exchanger?