Water hot but tepid after a few minutes

[tobee]

We have a hot water tank in our loft (new this year) and an immersion tank and a powerful electric pump that runs the gas heating which is run by a gas boiler on the ground floor. The immersion heater tank is two floors above the boiler.

Normally we have no issues but have noticed in the past few days that the hot water goes tepid after approximately three minutes.

So I stand by my shower eg to wait normal amount of time for the hot water to come through. Get in have 2/3 minutes of normal hot shower then it just goes tepid.

Is this likely something to do with the "mix" being wrong? The pump being at fault?

Have booked a gas engineer for next week but is it more likely to be the pump?

Bump

From your description I think you have a conventional gas boiler (not a flash boiler) so the tank in the loft is the cold water header tank and the "immersion" tank is the hot water tank. There will be an electric immersion heater element in that as a back up should the boiler fail.
When you've set the water to heat how long does the boiler stay on for and does the " immersion" tank get appreciably hotter? It sounds like the water is heating but not enough so either the boiler is cutting out early, not on long enough or the temperature setting is not correct.
If you can switch on the immersion heater (electric) and get the water hot enough for a shower, that will prove your pump is working and point to an issue with the boiler or with the settings.
Hope that helps

Thank you for your reply.

Hopefully the gas engineer will be able to help. Just wasn't sure if we needed them or needed a pump maintenance person. But the pump seems to be working.

Re reading your reply, the temperature gauge says the water is heating from whatever low temperature to the temperature set.

We have a hive set up and the water is set to come on twice a day for the same amount of time as it always has and there is also a boost facility for however long I chose to set it. This works (seemingly) as normal but then the water is still only hot for a short time as described above.

could be a partially blocked secondary heat exchanger. This transfers the heat from the radiator circuit to the hot water. The boiler will reduce the gas flow if the radiator circuit gets too hot then start up again once it is cooled down enough.

Does the shower get warm again after a bit or stay lukewarm indefinitely?

The other thing to check is your hot water taps - does the same thing happen with those ? If not it might be something to do with the way the shower is set up?

To answer questions -

I can't tell if it stays hot indefinitely because I get out before it gets too miserably tepid/cold

It comes out tepid everywhere as far as we can tell.

If its tepid out of the taps also then that would suggest a n issue with the boiler