27 Aug 2005
Reaction score
United Kingdom
I have a Worcester 15/19 Heatslave oil combi boiler with a twin channel programmer. We have 5 bar water pressure. The central heating is off for the summer. Recently, we have been having trouble getting consistent hot water, even with the Control Thermostat set to maximum and the heating period set to "on" constant. The boiler fires up normally when a hot tap or shower valve is opened. Sometimes the water gets scalding hot for a few moments, but then drops back to lukewarm. It can then be a long while before it gets hot again. However, the flow pipe from the boiler always seems very hot.
Any ideas? Many thanks! David
Sponsored Links
Er, Wil I think he means the mains is 5 bar??. not the system pressure.

Sludge in your secondary heat exchanger, probably. If it's the same as ye olde gas combi I've got a spare new one!


the boiler should fire up to keep the heatbank hot ,as well as on demand from tap.

is pump working?
Sponsored Links

Been to loads of these!

The Heatslave has a diverter valve which sends the primary water to the slave tank or the CH system. My guess is that the diverter has failed and does not open fully when the slave tank is in demand.

jim, dont the diverter valve spring back to dhw mode?

im not really clued up on errr anything,.... but particuliarly heatslave,
It depends how old it is! There are 3 different types of 3 port valve on the heatslave. I think two spring back to heating and the latest has a plunger pushing on a cylinder. At rest this is in hot water mode. However, it doen't really matter what diverter it is, they can still fail half way and not return.


DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local