Warmflow 70-90 hot water problems

[Shetlandplumber]

Hi all, first time poster here so hope you can help!

Got called to a boiler breakdown today with the customer complaining of lukewarm hot water. Had a look at the boiler and it is a warmflow 70-90 combi (with the flexible braided pipes inside)
I've seen before with them the flexible pipes being clogged with debris so I drained the boiler and checked but they are both clear. I thought it must then be the thermostatic mixer in the boiler so I replaced it with no success. I presumed the hot water circulating pump must not be moving enough water so I replaced it but that did not help either! The hot water is still running warm (48 oC) for a moment the lukewarm (38oC) after that.

The primary flow side of the plate heat exchanger is very hot, return side slightly colder and pipe from the heat exchanger to the mixing valve lukewarm. I called warmflow technical help and the suggested it must be the plate heat exchanger at fault but I though I would see if anyone here knew of anything else before ordering a new one. Some other threads have mentioned check valves in the pump housing? Any help is greatly appreciated!

Thanks!

 

[Bunker]

Get the boiler up to temp then open a hot tap. This should start the pump.
Check the primaries temps each side, if they are fairly similar then then primary is being pumped through the hex ok.
Compare the temp of the cold water into the hex Vs hot water out of it. This will tell you if the heat is being exchanged.
Run this for a while and see where any hot pipe goes cold.
If the primary goes cold then it could be the store is full of scale so not storing much hot water, if the primary goes cold, does the boiler kick in?
If its the hot water outlet pipe that goes cold before then primaries, then the hex is dead.

Is there a water softner? Is the water hard round there?

Anyone free to challenge the above, Im tired and probably not thinking clearly....

 

[Shetlandplumber]

Get the boiler up to temp then open a hot tap. This should start the pump.
Check the primaries temps each side, if they are fairly similar then then primary is being pumped through the hex ok.
Compare the temp of the cold water into the hex Vs hot water out of it. This will tell you if the heat is being exchanged.
Run this for a while and see where any hot pipe goes cold.
If the primary goes cold then it could be the store is full of scale so not storing much hot water, if the primary goes cold, does the boiler kick in?
If its the hot water outlet pipe that goes cold before then primaries, then the hex is dead.

Is there a water softner? Is the water hard round there?

Anyone free to challenge the above, Im tired and probably not thinking clearly....

Hi, thanks for the reply. I have not tried a thermometer on the pipes yet but the primary into the hex you cannot hold onto and the primary out is slightly colder. The boiler seems to be heating the store. The hot out if the hex is only lukewarm so it's like the heat isn't being exchanged? It's not a hard water area and the primary water in the boiler is very clean. Has anyone seen many problems with plate heat exchangers stopping exchanging?? Thanks!

 

[Bunker]

Ask the custard what their kettle is like, that will tell you everything.

 

[Ermintrude]

It's brand new, got it with new kitchen and bathrooms last week

 

[WHPES]

Does the water get hotter with the tap turned down? If so probably heat exchanger

What's the hardness of the water? Doesn't need to be really hard. Use a test tablet.

Either heat exchanger or supply pipework or the mixing valve (rarely the problem)