combi boiler problem

[Gilbert]

I have a Europa (Ideal Caradon) Combi wall-hung gas boiler. Perhaps a couple of months ago I noticed that the DHW flow to the kitchen tap (nearest to boiler) was getting low (approx half normal flow). As the DHW taps to shower/ bathroom were still working normally I checked the tap for a blockage, and considered replacing the pipework to the tap from where it tees off from the HW feed to the bathroom. But then I noticed a problem with the boiler - the thermostat settings are no longer graduated - i.e. the setting is either warm (minimum?) or very hot (maximum) with no in between on the dial ('very hot' kicks in around halfway on the dial). When on a warm setting the pressure stays relatively low - from 1.5bar cold to perhaps

2.5bar when in use - and relights in the morning when off overnight. But when the system is on a 'very hot' setting the pressure goes right up to nearly 4bar when in use, but overnight the pressure goes back down below 1bar so the boiler doesn't ignite in the morning. Any thoughts before I start delving...?

Thanks Gilbert

[John]

The pressure relates to the sealed part of the system and will rise as the water in the sealed system gets hotter. It will not have any effect on the tap. Are you sure that the tap was checked thoroughly. Is it a conventional one or a ceramic disc one?

[Gilbert]

"John" wrote

Yes, I realise that the system is sealed, I was just pointing out that the pressure rise had deviated from the norm recently and wondered if anyone had witnessed anything similar. I expect that the tap/boiler problems are almost certainly unconnected, but you never know! I checked the tap - a monobloc ceramic disc - and it seems in good order. Of course, I could be mistaken - perhaps I'll swap over the flexible H/C connections and see if that makes a difference. But my real interest lies with the boiler problem.

Cheers Gilbert

[John Rumm]

It sounds as if you may have two unrelated problems. The issue with regard to the system pressure rising too high sounds like lack of expansion room. The classic cause of this is the expansion vessel having either failed or at least being in need of pumping up.

This is all covered in detail here:

issue with the tap flow rate could be a number of problems. You did not mention where in the country you were or how hard the local water is, but one common problem that can lead to issues like this is the build up of scale in the plate heat exchanger that heats the hot water.

[bof]

In message , Gilbert writes

We're in a hard water area and had exactly this problem, it was due to lime scale in the corrugated flexible tail feeding the tap, cured by emptying the water out of the hot pipework and pouring in lime scale remover.

[Gilbert]

"bof" wrote

Thanks for that. I'll definitely check the flexible pipe for scale. Cheers Gilbert